Genetics Vocabulary:Gene:

A section of DNA that encodes a particular protein (ex: hair protein)

Alleles:Different versions of a gene (ex: black hair vs. blond hair)Everyone has two alleles for each gene – one from each parent!

Dominant:An allele that always shows up if you have it (ex: B = black hair)

Recessive:An allele that only shows up if there is no dominant allele (ex: b)

Genotype:The genetic make-up (combination of alleles) (ex: BB or Bb or bb)

Phenotype:The characteristics or traits that show up (ex: your hair color)

Genetics Vocabulary:Genotype:

The genetic make-up (combination of alleles) (ex: BB or Bb or bb)Phenotype:

The characteristics or traits that show up (ex: your hair color)Dominant:

An allele that always shows up if you have it (ex: B = black hair)Recessive:

An allele that only shows up if there is no dominant allele (ex: b)Homozygous: Two of the same allele for a particular trait are

present Ex: RR (homozygous dominant) = Red wings Ex: rr (homozygous recessive)= yellow wings

Heterozygous: Two different alleles for a particular trait are present Ex: Rr = red wings

Homozygous and Heterozygous Homozygous: Two of the same allele

for a particular trait are presentEx: RR (homozygous dominant) = Red

wingsEx: rr (homozygous recessive)= yellow wings

Heterozygous: Two different alleles for a particular trait are presentEx: Rr = red wings

More Genetics Vocabulary

Objectives for Class:• Experiment with probability to see the diversity of offspring that can be made through sexual

reproduction

Gregor Mendel – the “father” of genetics

Objectives for Class:• Use Mendel’s Principle of Segregation to explain: How can children show traits that their parents don’t have?

• Use Punnett Squares to solve monohybrid crosses

Traits that Mendel studied:

Objectives for Class:• Use Mendel’s Principle of Segregation to explain: How can children show traits that their parents don’t have?

• Use Punnett Squares to solve monohybrid crosses

Check Your Homework…Parents are true-breeding aka

homozygous2a. All F1 offspring showed one trait –

why? They all showed the dominant

phenotype because they all got a dominant allele from one parent

2b. They were all heterozygous3. What happened in the F2 generation?

The recessive trait reappeared in ¼ of the offspring

How can we explain this??

Mendel’s 1st Experiment

                              

Mendel’s Law of Segregation

Alleles segregate (separate) during meiosis so each gamete gets only one allele

a a A A

a Aa A

Two choices for gametes:

A or a

Another way to show this:

Aa

a AA a

Aa

AaAA aaAa

Start w/ Diploid CellsMeiosis:

Alleles separate into

different gametes

Punnett Squares show possibilites for

fertilization

Possible Gametes(Haploid)

Possible Diploid Zygotes – develop into offspring

Law of Segregation:Each gamete only gets

ONE allele for each gene

Principle of Segregation (continued…)

This explains why the recessive trait reappears in the F2 generation…

in ¼ of the offspring.

Punnett Squares (Predicting Probabilities)

Tongue rolling (R) is dominant over non-tongue rolling (r)

Two parents are both heterozygous. Write their genotypes!Mother is Rr Father is Rr

half of the sperm get each allele

½ of Mom’s eggs get the R allele

½ of Mom’s eggs get the r allele

R

r

rRRR

rr

Rr

Rr

Predicting ProbabilitiesThis Punnett Square is used to PREDICT

PROBABILITIES, NOT to tell you the actual numbers you will get!

Probability of Tongue Rolling (RR or Rr) = ¾ or 75%

Probability of Not rolling (rr)= ¼ or 25%

R

r

rRRR

rr

Rr

Rr

Using Punnett Squares to predict the sex of a child

Mother’s genotype: Father’s genotype: Make a Punnett Square and fill it in

Chances of girl (XX)

= ½ or 50%

Chances of boy (XY)

= ½ or 50%

X

YX

X

XX

XY

XY

XX

XXXY

Do Now #2: (in your notebook)

What is one difference between these two cells?

Which chromosome is homologous to this one? If we looked at human cells, how many pairs of

homologous chromosomes would they contain? Answer: 23 pairs (22 pairs plus the sex

chromosomes)

aaA A

b b

BB

a a A A

Cell 1Cell 2

Meiosis with Two Different Genes on

Two Different Chromosomes

                              

AB

A A aa

b bBB

A A aa

b b BB

AB

ab

ab

or…

aB

Ab

aB

Ab

Four different possible gametes:

AB ab Ab aB

Alleles for different genes segregate independently during meiosis.

In other words: If a gamete gets A or a, this doesn’t effect whether it gets B or b. Any combo is possible:Parent: AaBb

Possible gametes: AB Ab aB ab

This creates genetic diversity between gametes, and therefore a greater diversity of offspring.

Mendel’s Discoveries: Law of Independent Assortment

Objectives for Class:• Use Punnett Squares to solve dihybrid crosses• Use Mendel’s Principle of Independent Assortment to explain how genetic variation is

created in individuals.

Example: Dihybrid Cross (Two Traits)(only write what’s in purple)

Tall (T) is dominant over short (t)Black hair (B) is dominant over blond hair

(b)Two parents are heterozygous for both

traits:(1) Write the Parent Genotypes:

TtBb x TtBb(2) What Gametes can they make?

TB Tb tB tb

Tall w/ Black hair = Tall w/ Blond hair =

(3) Write the gametes along the sides of a BIG Punnett Square

(4) Use the Punnett Square to calculate probabilities!

TBTb

tB

tb

TB

Tb tB tb

TTBbTtBBTtBb

TTBB

Ttbb

TtBb

TTbb

TTBb

TtBB

TtBb

ttBB

ttBb ttbb

ttBb

Ttbb

TtBb

Short w/ Black hair = Short w/ Blond hair = 1/16

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