Genetics

Genetics is the scientific study of heredity and variation.

GeneticsIn asexual reproduction:•Single-celled organisms reproduce by simple cell division •There is no fertilization of an egg by a sperm

Asexual ReproductionFUNCTIONS OF CELL DIVISION

Sea stars

LM

Amoeba African Violet

Sexual reproduction requires fertilization of an egg by a sperm using a special type of cell division called meiosis.

Genetics

Genetics

Gregor Mendel•Worked in the 1860s•Was the first person to analyze patterns of inheritance•Deduced the fundamental principles of genetics

GeneticsRemovedstamensfrom purpleflower.

White

Stamens

Purple

Transferred pollen fromstamens of white flowerto carpel of purpleflower.

Parents(P)

Carpel

Offspring

(F1)

Pollinated carpelmatured into pod.

Planted seedsfrom pod.

Mendel studied garden peas because they:

•Easy to grow

• Come in many readily distinguishable varieties

• Easily manipulated

• Can self-fertilize

Genetics• A character is a heritable

feature that varies among individuals.

• A trait is a variant of a character.

• Each of the characters Mendel studied occurred in two distinct forms.

*P - parental generation*F1 – first filial generation*F2 – second filial generation

-Example:

X

Tall Dwarf

P

F1 – all Tall

Tall

F2

Genetics

Mendel’s hypotheses (to explain his results)

*genes and alleles

1. Alternative versions of genes (alleles) account for variation in inherited characters.

2. For each character, an organism inherits two alleles, one from each parent.

Genetics

3. If two alleles differ, one is dominant, the other recessive

X

Tall Dwarf

P:

DD dd

F1 – all Tall

TallDd

4. The two alleles for each character segregate (separate) during gamete production.

Mendel’s Law of Segregation

Genetics

GeneticsA Punnett Square predicts the results of a genetic cross between individuals of known genotype

D d d

Tall DwarfP: DD ddX

Gamete formation: D

*genotype

*phenotype

*Homozygous

*Heterozygous

D

D

d d

D d D d

D d D d

4/4 are Dd

4/4 are Tall

Genetics

Dihybrid cross- A genetic cross between two individuals involving two characters

GGWW ggww

Example:

P1

yellow, round

green, wrinkled

XGW GW GW GW

gw

gw

gw

gw

GgWw

Genetics

F1

All yellow, round

F1

All yellow, roundGgWw

F1

All yellow, roundGgWw

X

F2

9/16 yellow, round

3/16 yellow, wrinkled

3/16 green, round

1/16 green, wrinkled

GW Gw gW gw

gW

GW

gw

Gw

9:3:3:1 Phenotypic ratio; Genotypic ratio as follows:

1/16 GGWW, 2/16 GGWw, 2/16 GgWW, 4/16 GgWw1/16 GGww, 2/16 Ggww

1/16 ggWw, 2/16 ggWw

1/16 ggww

Mendelian inheritance is based on probabilityExample- coin toss

*1/2 chance landing heads

*Each toss is an independent event

*Coin toss, just like the distribution of alleles into gametes

*The rule of multiplication – determines the chance that two or more independent events will occur together

½ x ½ = ¼

B

B

b

Bb

b

Fem

ale

gam

etes B B

B

b b b

Male gametes

Formation of sperm

Bb male

Formation of eggs

Bb female

F2 Genotypes

F1 Genotypes

( )

12

14

12

12

12

14

14

14 1

212

Genetics

Female MaleAttachedFree

Third generation(brother and sister)

Second generation(parents, aunts, and uncles)

First generation(grandparents) Ff Ff

FfFF ff fforFf

ff FForFf

Ffff

Ff ff

Genetics: Pedigrees

Human Disorders