CHAPTER 25: MENDELIAN GENETICS

25-1: Mendel’s Principles of Heredity

The Study of Heredity

                Egg     +     Sperm  à     Zygote

                  n          +       n        à       2n

Zygote has all common _____________________________, but also its own distinct, ____________________________ that make it different from other members of the species.

Genetics:

Mendel’s Experiments –

He studied several traits, such as

·         

Pea plants normally _______________. When Mendel wanted to control pollination between 2 types of plants, he __________ _________________________________. He _____________ ______________________and ______________ to understand the results and _______________________.

What Mendel Did

Step 1:

This was the P (Parental) Generation

Step 2:

This is the F1 (First Filial) Generation

Step 3:

This is the F2 (Second Filial) Generation

Mendel’s Model

·         

·        

·       Dominant alleles are ______________ in an individual.

·       Recessive alleles may be present, but will _________ _____________ in the presence of a dominant allele

The Law of Dominance –

In Mendel’s F1 generation, ________ flower color was caused by a ___________________. The _____________________ for _________ flower color was ____________.

The Law of Segregation –

The Gene-Chromosome Theory – W.S. Sutton observed spermatogenesis and fertilization in grasshoppers

·       1903 paper, “_________________________________”

·         

·       The “__________” of Mendel’s theory were ___________ ____________________

·       __________________________, which are in a ________ __________ along each _______________

25-2: Fundamentals of Genetics

Alleles:

Alleles for a particular trait are found at the _______________ ___________________ of a pair of homologous chromosomes.

If a person is:

Homozygous Dominant,

(Ex: PP = Pure purple flower)

Homozygous Recessive,

(Ex: pp = Pure white flower)

Heterozygous,

(Ex: Pp = Hybrid purple flower)

Use letters to symbolize the alleles:

·       Upper case letter = ____________ allele (__) –________

·       Lower case letter = ____________ allele (__) –________

Probability

Toss a coin à chance of getting heads à _______

Toss a coin 100 times à chance of getting heads à ______

50 heads: 50 tails à _____ ratio

The ____________________________, the _______________ __________________ will be.

Law of Probability –

Punnett Squares –

Monohybrid Cross: ____________________ is studied.

·       Phenotype:

·       Genotype:

(the letters – ex: Pp)

Example: Cross a true breeding purple flower (PP) with a true breeding white flower (pp):

Genotypes:

Phenotypes:

Example: Cross two hybrid (Pp) flowers.

Genotypes:

Phenotypes:

Test Crosses –

Example: Cross a purple flower (P?) with a white flower (pp).

White flowers present à purple parent is ______________ (Pp)

All purple flowers à purple parent is _______________ (PP)

25-3: Other Concepts in Genetics

The Law of Independent Assortment –

Dihybrid Cross: A breeding exp’t involving _______________.

Mendel considered the following two traits in his dihybrid cross:

Shape of pea                               Color of pea

à       round (dominant) RR, Rr  à yellow (dominant) YY, Yy

à wrinkled )recessive) rr       à green (recessive) yy

P Generation:

F1 Generation:

F2 Generation:

·       9/16 yellow, round (YYRR, YyRR, YYRr)

·       3/16 yellow, wrinkled (Yyrr, Yyrr)

·       3/16 green, round (yyRR, yyRr)

·       1/16 green, wrinkled (yyrr)

Example: cross 2 heterozygous yellow, round peas (YyRr X YyRr)

Genotypes:

Phenotypes:

Incomplete Dominance –

___________________________________________ or completely hidden – a “___________” ______________.

In a Japanese 4 O’clock plant, red flowers are incompletely dominant over white.

RR à red;    RW à pink;        WW à white

Example: Cross a pink plant with a white plant:

Genotypes:                                    

Phenotypes:

Codominance –

(Roan coat in horses; blood types)

C^RC^R à red coat;   C^RC^W à roan coat;  C^WC^W à white coat

Example: Cross a red-coat horse with a roan-coat horse:

Genotypes:                             

Phenotypes:

Multiple Alleles –

I = ______________; i = ______________

_________________ stand for each _____________ allele

Example: Cross a person who is heterozygous Type A with a person who is Type AB.

Genotypes:

Phenotypes: