Unit 7 Meiosis and Mendel 8 Meiosis and...genotype of the parents, you can predict the likelihood of...
Transcript of Unit 7 Meiosis and Mendel 8 Meiosis and...genotype of the parents, you can predict the likelihood of...
Unit 8 Meiosis and MendelGenetics and Inheritance
Quiz Date: Jan 14
Test Date: Jan. 22/23
UNIT 8 - INTRODUCTION TO GENETICS
• Although the resemblance between generations of
organisms had been noted for thousands of years, it
wasn’t until the 1800s that scientific studies were
carried out to develop an explanation for this. Today
we know that we resemble our parents because of
_______________, which is the set of characteristics
we receive from ______________________. The
study of heredity is known as _________________.
heredityour parents
genetics
I. SEXUAL REPRODUCTION & MEIOSIS (pp. 275-278)
• In sexual reproduction, an egg and sperm cell
fuse together to create a fertilized egg or
_______________. zygote
A. Chromosome Number
1. Somatic Cells - _____________ cells•Human somatic cells contain ________ chromosomes•______________ or ________ meaning they contain a ____________ set of chromosomes, half ( _____ ) from _________ and half from ________. •“Matching” chromosomes known as ____________________.
•made up of a copy of a chromosome from each parent, with the same ___________, but they are ____________________.
•Somatic cells use ___________ for growth, development, renewal, and repair
Body46
Diploid 2ndouble 23Dad Mom
Homologous pairs
genes not identicalmitosis
Homologous Chromosomes
GAMETES
2. Gametes - ___________ and _______________
cells
• Human gametes contain ______ chromosomes.
• ______________ or ______ meaning there is
_____ set of instructions for each ______.
• When gametes fuse together in
_____________________, the ________________
produced is _____________ and has _______
chromosomes.
• Gametes are produced by a process called __________, rather than mitosis
Egg Sperm
23Haploid n
one gene
fertilization zygotediploid 46
meiosis
Haploid vs. Diploid
Karyotypes
B. Meiosis
• Special type of cell division that only occurs in
specialized germ cells (sex cells) in ____________
of females and ______________ of males.
• Before meiosis, DNA is replicated once (during
______ phase of ________________)…
• …But during meiosis cell divides
________________, resulting in ______ cells with
_______ the original chromosome number.
• Unlike mitosis which produces identical cells, meiosis produces genetically _____________ cells.
ovariestestes
2X, two times 41/2
S interphase
non-identical
Identical somatic cells Unique gametes
• Meiosis occurs in two stages:
1. Meiosis I
Prophase I➢Unlike in prophase of mitosis, In prophase I
___________________________ come together and
stick to each other to form a ______________.
Homologous pairstetrad
Meiosis I➢Crossing Over
▪ Exchange of genetic information between a
________________________________ with its
___________________________________.
▪ Occurs very frequently
▪ Allows for __________________________.
Sister chromatidNon-sister homologue
Genetic variation
Meiosis IMetaphase I
➢_____________________________ align in equator of cell
➢Each homologue consists of _______________________________________.
Anaphase I➢__________________________________________ are
pulled apart➢_________________, _________________________
still intact
Tetrads
Two sister chromatids
Homologous pairs
Centromeres Sister chromatids
Meiosis I Telophase I
➢Two cells are formed, each with _______ chromosomes
➢Each chromosome still composed of two
___________________
➢Two cells produced at the end of meiosis I are
_______________ because______________________
23
Sister chromatids
haploid There are no homologous pairs present
MEIOSIS II
2. Meiosis II
Prophase II
Continues with the two cells formed moving directly
into prophase II without any further
_____________________ of DNA.
Metaphase II
_______________ (not tetrads) composed of
__________________ are randomly aligned at the
equator of the cell.
replication
Chromosomes
Sister chromatids
2. Meiosis II
Anaphase II
Spindle fibers shorten
______________________ are pulled apart, just
like in anaphase of mitosis.
Telophase II
Four nuclei form around chromosomes, spindles
break down
Sister chromatids
2. Meiosis II
Cytokinesis II
Two new cells are formed from each of the two cells
formed in meiosis I, resulting in a total of
___________ new cells, each with
____________the original number of
chromosomes.
Cells produced are called ____________________.
41/2
Gametes
MEIOSIS
• In females, process is known as
________________________.
• In males, process is known as
_________________________.
oogenesis
spermatogenesis
3. Oogenesis vs. spermatogenesis
• Spermatogenesis: Males produce 4 viable sperm cells
• Begins:
____________
• Ends:
___________
puberty
death
3. Oogenesis vs. spermatogenesis
• Oogenesis: Females produce only one egg and 3 polar bodies
• Begins:
___________
• Ends:
___________
Before birth
menopause
Spermatogenesis vs Oogenesis
II. HISTORY OF GENETICS (pp. 263-270)
• A. Gregor Mendel
• Known as the “Father of _______________”• Famous for his experiments with ________ plants.
Geneticspea
Mendel• Used true-breeding pea plants, which means
________________________; characteristics
always show. Known as the ____________
generation.
• Studied seven ______________, including plant
height, seed color, flower color, etc. o A character is an ______________________________.
o A trait is a variant of a character
o Example: Eye color is a character, brown eyes or blue
eyes are traits
pureline, purebredP
characters
Inherited characteristic
Mendel
• Pea plants cross-pollinate, meaning pollen from
one plant fertilizes an egg from another, but they
can also self-pollinate, meaning pollen can fertilize
egg from ______________ plant. Mendel
controlled the fertilization process of the pea plants
by preventing
__________________________________ and
controlling
___________________________________.
same
Self-pollination
Cross-pollination
Pea Traits Studied
•
B. Mendel’s Results
• P generation – Crossed __________________ plants with one trait with ________________ plants with the other.
• For example, _____________________________________________
• F1 generation – Offspring produced from _________________. In F1, one trait ____________. For example, tall plants X short plants = __________________________.
• F2 generation – Offspring produced from _________________. In F2, trait that disappeared in F1reappeared in __________ of the offspring; the other ¾ showed _____________________________.
True-breedingTrue-breedingTT (tall) x tt (short)
P X P disappeared
All tall plants
F1 X F11/4
Dominant trait
•
Mendel’s Principles
• C. Mendel’s Principles – After analyzing his
results carefully, Mendel formed conclusions that
increased understanding of inheritance and opened
the door for the study of genetics.
• Individual units called ___________ determine
inheritable characteristics. A gene is a portion of
___________ that codes for a specific ____________.
genes
DNAtrait
Alleles and Genes
Mendel’s Principles
• For each gene, an organism inherits two alleles, one from each __________________. Alleles are different forms or ____________________ of a ___________. For any given trait,o If an organism is ___________________ (for a gene), its alleles
are the same and the trait will be expressed.o If the alleles differ, the organism is said to be
___________________ for that character and only one allele will be expressed. The expressed allele is the ______________ allele, designated by an __________-case letter. The allele that is not expressed in a heterozygous trait is _________________, designated by a _____________-case letter. A recessive allele is only expressed when an organism is ________________ for that gene.
parentversions gene
homozygous
heterozygousdominant
upperrecessive
lowerhomozygous
Mendel’s Principles
• Principle of Segregation - In meiosis, the two alleles for a trait segregate (_______________). Each egg or sperm cell receives a copy of one of the two alleles present in the somatic cells of the organism. There is a _________ chance that a copy of that allele will end up in the gamete produced.
• Principle of Independent Assortment – The way one pair of alleles segregates has no influence on any other pair of alleles.
separate
50%
Independent Assortment
D. Genetics Terminology
• 1. Phenotype - ________________ description of
trait; for example, ______________
• 2. Genotype – Genetic make-up of an organism or
set of alleles; for example, ____________________.
Physical
Tall, short
TT, Tt, heterozygous, etc..
Genetics Terminology
• 3. Application of Terminology - If round pea seeds are dominant to wrinkled pea seeds, round is designated _____ and wrinkled is designated ______.• a. Homozygous dominant• Genotype = ________; Phenotype = ________• b. Heterozygous• Genotype = ________; Phenotype = ________• c. Homozygous recessive • Genotype = ________; Phenotype = ________
Rr
RR round
Rr round
rr wrinkled
III. ANALYZING INHERITANCE (pp.135-137)
• A. Probability
Due to the law of_______________, if you know the
genotype of the parents, you can predict the likelihood
of a trait occurring in the offspring. Probability can be
written 3 ways. The probability of a coin coming up
heads after being flipped is (fraction) _____, (ratio) ________, or (percent) _______.
segregation
1/21:1 50%
B. Punnett Squares• A Punnett square is a tool used to predict the
possible outcomes of _______________ and
____________________; in other words, a Punnett
square is used to determine the probability of certain traits appearing in offspring.
meiosisfertilization
Punnett Practice Monohybrid crosses A-D
• Must have a key
• And Cross with
• Each problem
• For full credit
A: Construct a Punnett square to determine the probability of white flowers is a heterozygous purple
flower (Pp) is crossed with a homozygous white flower (pp)
1. Key:________________________
2. Cross:________________
Probability of White flowers:___________50%
P=purple, p=white
Pp X pp
P p
p
p
Pp pp
Pp pp
B: Construct a Punnett square to determine the probability of short pea plants if a homozygous tall
plant (TT) is crossed with a heterozygous tall plant (Tt)
1. Key:__________________
2. Cross:________________
Probability of short pea plants:___________
Probability of tall pea plants:___________
T=tall, t=short
TT X Tt
T T
T
t
TT TT
Tt Tt
0%
100%
C: If round peas are dominant over wrinkled peas, make a Punnett square to determined the genotype
and phenotype ratios of the offspring if a heterozygousplant is crossed with a homozygous recessive plant
1. Key:__________________
2. Cross:________________
R=round, r=wrinkled
Rr X rr
R r
r
r
Rr rr
Rr rr
RR:Rr:rr 0:2:2
2:2
Genotypic ratio:__________________
Phenotypic ratio:_________________
D: Use a Punnett square to determine the genotype and phenotype ratios of the offspring from a cross
between a homozygous dominant yellow pea plant and a homozygous recessive green pea plant
1. Key:__________________
2. Cross:________________
Y=yellow, y=green
YY X yy
Y Y
y
y
Yy Yy
Yy Yy
YY:Yy:yy 0:4:0
4:0
Genotypic ratio:________________
Phenotypic ratio:_________________
Dihybrid crosses
The punnett squares we have been doing are known as ____________________ crosses, meaning that only one traits has been considered at a time. In a dihybrid cross, __________ different ______________ on 2 different _____________ are analyzed.
monohybrid
2
genes
chromosomes
Punnett Practice dihybrid crosses A-B
1. Key
2. Cross
3. Punnet square
A. Peas homozygous for round shape and heterozygous for color are crossed with
heterozygous yellow peas, heterozygous for shape
Key: R=round, r=wrinkled
Y=yellow, y=green
Cross: _____________________
Genotypic
ratio:_______________________
___________________________
_________
Phenotypic ratio:
___________________________
__________________________
B. Key: G= gray body, g= black body;
R=red eyes, r =black eyes
Cross: GGRr X Ggrr
What are the phenotypes of the
parent fruit flies:
___________________________
________________________
Genotypic ratio:
___________________________
________________________
Phenotypic ratio:
___________________________
__________________________
Incomplete Dominance
• Neither allele has “complete” dominance over the other; heterozygous phenotype is a blendof the 2 homozygous phenotypes
• Ex: snapdragons
R = red
W = white
RW = pink
Incomplete Dominance: cross a pink snapdragon with a white snapdragon
1. Key: _________________________
2. Cross: ________________________
Phenotypic ratio:___________________
Genotypic ratio:____________________
Incomplete Dominance: cross a red snapdragon with a white snapdragon
1. Key: _________________________
2. Cross: ________________________
Phenotypic ratio:___________________
Genotypic ratio:____________________
Codominance• Codominance – Both alleles share dominance and
are always expressed if present.
• Ex: In chicken
B = black feathers
W = white feathers
BW = black AND white
feathers
X
Codominance: cross a black chicken with a black and white chicken
1. Key: _________________________
2. Cross: ________________________
Phenotypic ratio:___________________
Genotypic ratio:____________________
Codominance: cross a white chicken with a black and white chicken
1. Key: _________________________
2. Cross: ________________________
Phenotypic ratio:___________________
Genotypic ratio:____________________
Polygenic Traits
• “Many genes” ; Many traits are controlled by more than one gene; have a variety of choices for expression.
• Ex: _hair color, eye color, skin tone
Multiple Alleles
• Many genes that have more than 2 alleles, although an individual only has 2 alleles for the gene.
• Ex: blood group.
• There are 3 possible
• alleles for this gene.
Suggested study questions
• p. 283 (1-5, 11, 12, 17-20)