Genetics_Zoology_Part_1

7/30/2019 Genetics_Zoology_Part_1

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Mendelian Inheritance

Part 1

Prepared By: Asst. Prof.Sheryl Santa Cruz- Biscocho


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Gregor Mendel

1823-1884

Father of

Genetics

Monk in Austria

Experimented

with garden peas


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Short

Tall

Tall


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Mendels Hypotheses

Each parent has two factors (alleles)

Each parent gives one of those factors to the

offspring Tall has TT

Short has tt

Tall is DOMINANT Short is recessive


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TT tt

T t

Tt


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TT TT

T T

TT


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tt tt

t ttt


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Law of Segregation

Alleles separate during gamete production

Gametes have one allele for each trait

During fertilization gametes combine at

random to form individuals of the next

generation


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Discovery of Chromosomes in 1900

Confirmed Law of Segregation Chromosomes

are in pairs

Each chromosome hasone of the allele pair


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Chromosomes line up in a

double row.

Meiosis Metaphase

Assume a T allele on each red chromatid and a t

allele on each blue chromatid

T T t t


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Chromosomes separate

Each each daughter cell getsdoubled chromosomes

T Tt t


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Doubled Chromosomes Separate

in Second Meiotic Division

T T t t


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Each gamete will have a T allele or a t

allele

T T t t


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Allele

Member of a paired gene

One allele comes from each parent

Represented by a single letter


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Dominant & Recessive

Alleles Dominant alleles are expressed

Recessive alleles are not expressed in the

presence of a dominant allele

Recessive alleles are only expressed if both

recessive alleles are present


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Gene

A unit of heredity that controls the

development of one trait

Made of DNA

Most genes are composed of two alleles


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Homozygous

Both alleles alike

AA or aa


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Heterozygous

Alleles are different

Aa


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Genotype

Genetic make up

Represented by alleles

TT & Tt are genotypes for TALL pea plants


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Phenotype

A trait

Genotype determines the phenotype

Tall is a phenotype


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Homologous Chromosomes

Chromosomes of the same pair

Each homologue will have one allele for a

paired gene

Homologous chromosomes pair up during

meiosis

Only one of each homologue will be in each

gamete


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Sickle Cell Anemia

RBCs sickle shaped

Anemia

Pain

Stroke

Leg ulcers

Jaundice

Gall stones

Spleen, kidney & lungs


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Sickle Cell Anemia

Recessive allele s, codes for hemoglobin S

Long rod-like molecules

Stretches RBC into sickle shape

Homozygous recessive ss, have sickle cell

anemia

Heterozygous Ss, are carriers


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Albinism

Lack of pigment

Skin

Hair Eyes


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Amino Acids Melanin PigmentEnzyme

A a

AA = Normal

pigmentation

Aa = Normalpigmentation

aa = Albino


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PKU Disease

Phenylalanine excess

Mental retardation if

untreated


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Phenylalanine TyrosineEnzyme

P p

PP = Normal

Pp = Normal

pp = PKU


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If a man & woman are both carriers

(heterozygous) for albinism. What is

the chance their children will inherit

albinism? Solve using punnet square

use letter a.

Monohybrid Cross or One Trait


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AA = Normal

pigmentation

Aa = Normalpigmentation

(carrier)

aa = Albino

Man = Aa Woman = Aa

A

a a

A


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A

a

a

A AA

Aa

Aa

aa


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AA

Aa

Aa

aa

Genotypes

1 AA, 2Aa, 1aa

Phenotypes

3 Normal

1 Albino

Probability

25% for albinism


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If a man & woman are both

carriers (heterozygous) for PKU

disease. What is the chance their

children will inherit PKU disease?


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p

p

P PP

Pp

Pp

pp

P

PP = Normal

Pp = Normal

(carrier)

pp = PKU disease


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PP

Pp

Pp

pp

Genotypes

1 PP, 2Pp, 1pp

Phenotypes

3 Normal

1 PKU disease

Probability

25% for PKU disease


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If a man with sickle cell anemia

marries a woman who is a carrier.

What is the chance their children

will inherit sickle cell anemia?


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s

s

s Ss

Ss

ss

ss

S

SS = Normal

Ss = Normal

(carrier)

ss = Sickle Cell


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Ss

Ss

ss

ss

Genotypes

2 Ss, 2ss

Phenotypes

2 Normal (carriers)

2 Sickle cell

Probability

50% for Sickle cell


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Dwarfism = D

Normal height = d

DD = Dwarfism

Dd = Dwarfism

dd = Normal height

Dwarfism

Dwarf Band
http://www.quigsmss.com/kingzhomepage.htmhttp://www.quigsmss.com/kingzhomepage.htm


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A man with heterozygous

dwarfism marries a woman who

has normal height. What is thechance their children will inherit

dwarfism? Dwarfism is dominant.


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d

d

D Dd

dd

Dd

dd

d

DD = Dwarf

Dd = Dwarf

dd = Normal


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Dd

dd

Dd

dd

Genotypes

2 Dd, 2dd

Phenotypes

2 Normal

2 Dwarfs

Probability

50% for Dwarfism


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Law of Independent Assortment

The inheritance of one gene does not

influence the inheritance of another gene if

they are on separate chromosomes. The gene for albinism does not affect the

gene for dwarfism


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Dihybrid Cross or Two Traits

A heterozygous tall plant that is also

heterozygous for yellow seeds is crossed

with another plant with the same genotype Tall and yellow seeds are dominant to short

and green seeds.


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Tall Yellow

TtYy

TY

What gametes can each parent produce?

Ty

tYty

TtYy

TY

Ty

tYty

Tall Yellow


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9 Tall-Yellow

Match gametes on a Punnent Square

TY

Ty

tY

ty

TY Ty tY ty

TtYy

TtYy

TTYY TTYy TtYY

TTYy TTyy Ttyy

TtYY TtYy ttYY ttYy

TtYy Ttyy ttYy ttyy

3 Tall-Green

3 Short-Yellow

1 Short-Green


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A man with blue eyes and normalheight marries a woman with

heterozygous brown eyes and

heterozygous dwarfism. What arethe possible phenotypes of their

children? Dwarfism & brown eyes

are dominant.


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Normal height-Blue

ddbb

db

What gametes can each parent produce?

DdBb

DB

Db

dBdb

Dwarf-Brown


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DB

Db

dB

db

Match gametes on Punnent Square

db

DdBb

Ddbb

ddBb

ddbb

Dwarf-Brown eyes

Dwarf-blue eyes

Normal height-Brown eyes

Normal height-Blue eyes


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X-linked Traits

Alleles on the X chromosome

Women have two alleles

Men have one allele


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Hemophilia

Blood clotting impaired

Recessive allele, h

carried on X cmsX-linked recessive trait

More common in males


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XH XH = Normal Female

XH Xh = Normal Female

(Carrier)

Xh Xh = Hemophiliac Female

XH

y = Normal MaleXhy = Hemophiliac Male

Alleles must be written on X

chromosome


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A man with hemophilia marries a

normal woman who is not a

carrier. What is the chance theirchildren will inherit hemophilia?

Hemophilia is X-linked recessive.



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y

XH

Xh XH Xh

XH


(Carrier)


XHy = Normal Male

Xhy = Hemophiliac Male

XH Xh

XHy XHy

X

XH


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Genotypes

2 XH Xh, 2XHy

Phenotypes

2 Carrier Females

2 Normal Males

Probability

O% for Hemophilia

y

H

Xh XH Xh XH Xh

XHy XHy


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A normal man marries a normal

woman who is a carrier for

hemophilia. What is the chancetheir children will inherit

hemophilia?



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y

Xh

XH

XH


(Carrier)


XHy = Normal Male

Xhy = Hemophiliac Male

XH XH XH Xh

XHy Xhy

XhXH


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Genotypes

1XH XH, 1XH Xh,

1XHy, 1 Xhy

Phenotypes

2 Normal Females

1 Normal Males

1 Male Hemophiliac

Probability50% for Male Hemophiliac

0% for Female Hemophiliac

y

XH XH XH XH Xh

XHy

X

h

y


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Hypertrichosis

X-linked dominant

Similar gene in apes

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