Daily Agenda

• Daily Trivia

• Agenda

• Check Homework

• Notes on Genetic Crosses

• Groupwork on HW worksheets

• Homework

RR / BIO 137

What is genetics?• Genetics is the study

of HOW traits are passed from parents to offspring.

– Offspring show some traits of each parent

– These traits from parents are passed onto the offspring by sex cells

Body Cell vs. Sex Cell

Body Cell Sex Cell

make up most of the tissues and organs in

body

sperm or egg cell only

Has 23 pairs of chromosomes

(total=46 chromosomes)

Has 23 chromosomes

The chromosomes are paired up

Only 1 of each chromosome

Chromosomes

BODY CELL SEX CELL

Genes• A gene is a small

section of chromosome that determines a specific trait

• Genes are arranged on a chromosome

• Each chromosome carries specific genes

gene

Ch

rom

oso

me

Genes

• The genes on chromosomes in body cells are paired

–2 genes represent a trait in each body cell

Pair of chromosomes

Gene 1 Gene 2

Same Trait

Fertilization

• FERTILIZATION: we get genes from each of our parents

• The only way traits are passed onto offspring

MOM DAD

Offspring

Dominant Genes

• Genes that keep other genes from showing their traits

• EX: plant size• “T” is for the tall

gene for a tree

• Uppercase letters only

Recessive Genes

• The genes that do not show their traits when dominant genes are present

• Lowercase letters only

EX: plant size

“t” is the gene for a short tree

Dominant vs. Recessive

• Pure Dominant – an organism with 2 dominant genes for a trait

• Pure Recessive – an organism with 2 recessive genes for a trait

• Heterozygous – an organism with 1 dominant and 1 recessive gene for a trait– The dominant gene will overpower the recessive

gene.– The dominant gene will be expressed

Example: Palm Tree Height

Dominant RecessiveGene is

depicted with a capital letter

Ex: T

Gene is depicted by a

lower case letter

Ex: t

TT = pure dominant

tt = pure recessive

Tt = heterozygous

TTorTt

tt

TALL SHORT

Punnett Square

• A way to show which genes can combine when and egg and sperm join

• Letters are used in place of genes

• Large letter = dominant gene (F)

• Small letter = recessive gene (f)

Mother’s Genes

Fa

the

r’s

Gen

es

Homework

• p. 11-12

• 211s

Daily Trivia

• Elephants can “hear” through their feet.

Agenda

• DT

• Agenda

• HW Check

• Finish Notes

• Punnett Squares

• Homework

Punnett Square

• Large letter goes first in heterozygous organisms (Ff)

• Let’s do a cross between a pure dominant male (sperm) for free earlobes (FF) and a female (egg) who is heterozygous for free earlobes (Ff)

FF Ff

FF Ff

F

F

F f

F is dominant over f

What are the expected results?

FF

Free Earlobes

Ff

Free

Earlobes

Ff

Free

Earlobes

ff

Attached

Earlobes

F

f

F f

Expected vs. Observed Results

Expected ObservedCan be calculated Actually seen

Predicted Not Predicted

Genotype: The combination of genes

one has

Phenotype: the physical trait that you can see

What you expect to observe

What you actually observed

Dominant/Recessive

• One allele is dominant over the other (capable of masking the recessive allele)

PP = purple pp = white Pp = purple

Problem: Dominant/Recessive• In pea plants, purple flowers (P) are dominant

over white flowers (p) show the cross between two heterozygous plants.

P

p

P p

pp

Pp

Pp

PP- PP (1); Pp (2); pp (1)- ratio 1:2:1

- purple (3); white (1)- ratio 3:1

GENOTYPES:

PHENOTYPES:

Punnett Square• 5 Steps

– Type of cross– Key– Cross– Square– Answer the question

• Practice Problems on the board

• Pages 13-16

Homework• 2 Worksheets