GeneticsGenetics——Branch of biology that Branch of biology that studies hereditystudies heredity

Heredity – Heredity – the passing on of the passing on of characteristics from parents to characteristics from parents to offspringoffspring

Gregor Mendel--Gregor Mendel--Austrian monk Austrian monk who used pea plants to study how who used pea plants to study how traits are passed from one traits are passed from one generation to the nextgeneration to the next

TraitsTraits——characteristics that are inheritedcharacteristics that are inherited

HybridHybrid——offspring of parents (pea plants) offspring of parents (pea plants) that have different forms of a traitthat have different forms of a trait Ex.Ex.——tall pea plant bred with short pea planttall pea plant bred with short pea plant

Mendel bred tall pea plants withMendel bred tall pea plants with short short plantsplants The offspring in the 1The offspring in the 1stst generation were all generation were all talltall The offspring in the second generation were 75% The offspring in the second generation were 75%

talltall and 25% and 25% shortshort The short trait disappeared in the The short trait disappeared in the 11stst generation generation and and

reappeared in the reappeared in the 22ndnd generation generation

Mendel’s ExperimentMendel’s Experiment Cross-pollination—using pollen from one plant Cross-pollination—using pollen from one plant

to pollinate a different plantto pollinate a different plant

•P generation—original parents

•F1 generation—offspring of the parent plants (filial)

•Ex.Your parents are P and you are F1

Short pea plantShort pea plant Tall pea plantTall pea plant

All tall pea plantsAll tall pea plants

3 tall: 1 short3 tall: 1 short

PP11

FF11

FF22

AllelesAlleles——Different forms of the same Different forms of the same gene, each one located on different gene, each one located on different copies of the same chromosome (1 from copies of the same chromosome (1 from mother and 1 from father)mother and 1 from father) Ex. Ex. T is allele for tall plant, t is allele for T is allele for tall plant, t is allele for

short plantshort plant

•Dominant—trait that covers over another trait, capital letter

•Ex. T (tall) is a dominant allele

•Recessive—trait that is covered over by another trait, lower case letter

•Ex. t (short) is the recessive allele

T-tall t-short

The second generationThe second generation

Recessive Recessive traittrait

Dominant Dominant traittrait

Seed Seed shapshap

ee

SeeSeed d

colocolorr

FloweFlower r

colorcolor

Flower Flower positionposition

Pod Pod colorcolor

Pod Pod shapeshape

Plant Plant heightheight

rounroundd

yellowyellow purplepurpleaxial axial (side)(side) greengreen inflatedinflated talltall

wrinkledwrinkled greengreen whitewhiteterminal terminal

(tips)(tips) yellowyellow constrictedconstricted shortshort

•Phenotype—physical appearance

•Ex. Phenotype is tall

•Genotype—genetic makeup

•Ex. Genotype can be TT for a tall plant

Tall pea plant

•Homozygous—2 same alleles for a trait

•Ex. TT-tall tt-short

•Heterozygous—2 different alleles for a trait (carrier)

•Ex. Tt-tall TT, Tt-tall tt-short

Simple Genetic Human TraitsSimple Genetic Human Traits

Tongue Rolling (R)Tongue Rolling (R)Dimples (D)Dimples (D)Freckles (F)Freckles (F)Eye Color: Brown is dominant to blue Eye Color: Brown is dominant to blue

(B)(B)Hitchhiker’s Thumb (h)Hitchhiker’s Thumb (h)

Law of segregationLaw of segregation——Each gene has 2 Each gene has 2 alleles for a trait, after meiosis each alleles for a trait, after meiosis each gamete receives one of these allelesgamete receives one of these alleles

Law of Independent assortmentLaw of Independent assortment – – genes for different traits are genes for different traits are independently inherited of each otherindependently inherited of each other

Punnett squarePunnett square----A tool used to A tool used to predict the possible offspring of a predict the possible offspring of a cross between 2 parentscross between 2 parents

Monohybrid crossMonohybrid cross----crossing a crossing a single trait between 2 parentssingle trait between 2 parentsGenotype of the parents along top Genotype of the parents along top

and side of squareand side of squareCross each trait individuallyCross each trait individually

1. Cross TT x tt1. Cross TT x tt T T

t

t

Tt Tt

Tt Tt

Genotypic ratio100% Tt

Phenotypic ratio100% tall

2. Cross Tt x tt2. Cross Tt x tt2. Cross Tt x tt2. Cross Tt x tt T t

t

t

Tt tt

Tt tt

Genotypic ratio50% Tt 50% tt1 Tt : 1 tt

Phenotypic ratio50% tall 50% short1 tall : 1 short

3. Cross Tt x TT3. Cross Tt x TT T t

T

T

TT Tt

TT Tt

Genotypic ratio50% TT 50% Tt1 TT : 1 Tt

Phenotypic ratio100% tall

4. Cross Tt x Tt4. Cross Tt x Tt4. Cross Tt x Tt4. Cross Tt x Tt T t

T

t

TT Tt

Tt tt

Genotypic ratio25% TT 50% Tt 25%tt1 TT : 2 Tt : 1 tt

Phenotypic ratio75% tall 25% short3 tall : 1 short

Female (eggs): XXFemale (eggs): XXMale (sperm): XYMale (sperm): XY

Sex ChromosomesSex Chromosomes•

Every time a female has a

baby, what percent chance do

they have of having a boy?

A girl?

•If a female has 5 boys in a

row, what percent chance do

they have to have another boy?

A girl?

•Which parent determines the

sex of a baby? WHY?