Genetics Chapter 12. 12-1: Origins of Hereditary Science.
-
Upload
kristina-norman -
Category
Documents
-
view
216 -
download
0
Transcript of Genetics Chapter 12. 12-1: Origins of Hereditary Science.
Genetics
Chapter 12
12-1: Origins of Hereditary Science
Mendel’s Experiments
Genetics – The study of how characteristics are transmitted from parents to offspring
Heredity – The passing on of genetic characteristics from one generation to another
Mendel’s Experiments
Gregor Mendel (an Austrian monk) used cross-pollination techniques in which pollen is transferred between flowers of two different plants.
Mendel’s Experiments
Reasons Mendel used pea plants Require little care Produce many offspring Mature quickly (8-10 weeks)
Mendel’s Experiments
P (parental) generation – Organisms that are true-bred for specific traits
F1 generation – Offspring of the P generation
F2 generation – Offspring of the F1 generation F = Filial (pertainting to a son or daughter)
Mendel’s Experiments
Self-pollination – A plant with both male and female reproductive organs that fertilizes itself
Cross-pollination – Pollen from one plant is carried to the flower of another plant
Mendel’s Experiments
Three Steps of Mendel’s Experiments
Mendel’s Experiments
Gene – A section of DNA that carries the information on how to make one protein
Mendel’s Experiments
Allele – An alternative form of a gene
One allele for each trait is passed from each parent to the offspring.
Mendel’s Experiments
Dominant trait – An allele that is fully expressed whenever the allele is present in an individual The trait that masks the
other Recessive trait – An allele
that is expressed only when there is no dominant allele present in an individual The trait that is masked
12-2: Genetic Crosses
Monohybrid Cross
Monohybrid cross – A cross in which one characteristic is tracked
Punnett square – used to predict the outcome of genetic crosses
Monohybrid Cross
Genotype – the genetic makeup of an organism (use letters)
Phenotype – the appearance of an organism (physical appearance)
Monohybrid Cross
Homozygous – having identical alleles Heterozygous – having different alleles
Monohybrid Cross
Trait – Plant height Phenotype
T – tall t – short
Genotype TT – homozygous
dominant (pure bred) Tt – heterozygous
(hybrid) tt – homozygous
recessive (pure bred)
Monohybrid Cross
Probability – the likelihood that a specific event will occur
Probability = number of one kind of possible outcome
total number of all possible outcomes
A probability may be expressed as a decimal, a percentage, or a fraction
Mendel’s Characteristics
Monohybrid Cross
Ratios and percentages TT x tt = 100% heterozygous TT x TT = 100% homozygous dominant tt x tt = 100% homozygous recessive Tt x tt
50% heterozygous 50% homozygous recessive
Monohybrid Cross
Ratios and percentages Tt x Tt = Genotypic ratio – 1:2:1 ratio
25% homozygous dominant 50% heterozygous 25% homozygous recessive
Tt x Tt = Phenotypic ratio – 3:1 75% tall 25% short
Dihybrid Cross
Dihybrid cross – A breeding experiment that tracks the inheritance of two traits
Example Traits: Seed shape & Seed color Alleles: R – round
r – wrinkled Y – yellow y – green
Dihybrid Cross
Use the FOIL method for each parent to set-up the Punnett square
RrYy x RrYy
RY Ry rY ry RY Ry rY ry
Dihybrid Cross
RY
Ry
rY
ry
RY Ry rY ry
24
RRYY
RRYy
RrYY
RrYy
RRYy
RRyy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
Round/Yellow: 9
Round/green: 3
wrinkled/Yellow: 3
wrinkled/green: 1
9:3:3:1 phenotypic ratio
RY Ry rY ry
RY
Ry
rY
ry
Dihybrid Cross
This chart is used to illustrate the variety of eye colors
The trait for eye color actually has three alleles:
AaBbCc
Why eye color changes in people is unknown
Other Monohybrid Crosses
Incomplete dominance – a form of intermediate inheritance in which one allele for a specific trait is not completely dominant over the other allele This results in a
combined phenotype.
Other Monohybrid Crosses
Codominance – Two alleles are expressed (multiple alleles) in heterozygous individuals Two alleles that are both dominant
Example: blood typesKey
A = IA
B = IB
O = I
A and B are dominant over O
Other Monohybrid Crosses
Genotypes Phenotypes Type A = IAIA or IAi AA or AO Type B = IBIB or IBi BB or BO Type AB = IAIB AB Type O = ii OO
Other Monohybrid Crosses
Sex-Linked traits – Traits (genes) located on sex chromosomes X – Female sex chromosome Y – Male sex chromosome
Many sex-linked traits carried on X chromosome
Pedigree
Pedigree – A diagram of family relationships that uses symbols to represent people and lines to represent genetic relationships