Chapter 11

Introduction to Genetics

IV. MEIOSIS

• Mendel’s principles require 2 things-1)each organism inherits a single copy for every gene from each parent.

• 2)When an organism produces its own gametes,those 2 sets of genes must be separated from each other so that each gamete has only 1 set.

Analyzing Inheritance

• Offspring resemble their parents. Offspring inherit genes for characteristics from their parents. To learn about inheritance, scientists have experimented with breeding various plants and animals.

• In each experiment shown in the table on the next slide, two pea plants with different characteristics were bred. Then, the offspring produced were bred to produce a second generation of offspring. Consider the data and answer the questions that follow.

Section 11-1

Interest Grabber

I. The work of Gregor Mendel

• _____________________=The scientific study of heredity.

genetics

• 1. In the first generation of each experiment, how do the characteristics of the offspring compare to the parents’ characteristics?

• 2. How do the characteristics of the second generation compare to the characteristics of the first generation?

Section 11-1 Interest Grabber continued

Parents

Long stems short stems

Red flowers white flowers

Green pods yellow pods

Round seeds wrinkled seeds

Yellow seeds green seeds

First Generation

All long

All red

All green

All round

All yellow

Second Generation

787 long: 277 short

705 red: 224 white

428 green: 152 yellow

5474 round: 1850 wrinkled

6022 yellow: 2001 green

A. Gregor Mendel’s Peas

– Austrian monk whose statistical work w/ pea plants yielded a greater understanding of biological inheritance

– He knew each flower produces pollen,containing the male reproductive cells-sperm and female portion produces egg cells.During sexual reproduction,male and female cell join in ________-making a new cell that develops into an embryo

– Pea plants self-pollinating

fertilization

– He started w/ true-breeding plants-meaning that if they are allowed to self-pollinate,they make offspring _________ to themselves.

• 1 group ____ plants• 1 group ______• 1 made only ______ seed• 1 made ______ seeds

tall

shortgreen

yellow

identical

• Mendel wanted to produce seeds from male and female reproductive cells from 2 different plants,preventing self-pollination by cross-pollination,with 2 different plants as parents….This allowed him to cross- breed characteristics

B. Genes and Dominance

• Mendel studied different characteristics.• These characteristics are called

______________-such as seed or flower color or height in humans

• Studied 7 traits-see p.264-and he studied the offspring

• The offspring are called F1(“first filial”…Filius and filia are Latin words for son and daughter)

• __________________are the offspring of crosses of parents w/different traits.

• Mendel expected characteristics to blend-like red+white=pink-This was not the outcome

Traits

hybrids

• 2 conclusions:– 1) biological inheritance is determined by

factors carried by one generation to another.we now call these chemical factors that determine traits___________________.

• Different forms of a gene are called ___________________

genes

alleles

– 2) The Principle of Dominance states some alleles are ________________and some are recessive

• Alleles occur in pairs and only one allele w/ a certain trait needs to be present for a _________________trait

• 2 alleles of that trait must be present for _______________traits.

• Tall plants were dominant and short recessive.

dominantdominant

recessive

Seed Shape

Flower Position

Seed CoatColor

Seed Color

Pod Color

Plant Height

PodShape

Round

Wrinkled

Round

Yellow

Green

Gray

White

Smooth

Constricted

Green

Yellow

Axial

Terminal

Tall

Short

Yellow Gray Smooth Green Axial Tall

Section 11-1

Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants

P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Section 11-1

Principles of Dominance

P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Section 11-1

Principles of Dominance

P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Section 11-1Principles of Dominance

Tossing Coins• If you toss a coin, what is the probability of getting heads? Tails? If you toss a coin 10 times, how many heads and how many tails would you expect to get? Working with a partner, have one person toss a coin

• ten times while the other person tallies the results on a sheet of paper. Then, switch tasks to produce a separate tally of the second set of 10 tosses.

Section 11-2

Interest Grabber

1. Assuming that you expect 5 heads and 5 tails in 10 tosses, how do the results of your tosses compare? How about the results of your partner’s tosses? How close was each set of results to what was expected?

2. Add your results to those of your partner to produce a total of 20 tosses. Assuming that you expect 10 heads and 10 tails in 20 tosses, how close are these results to what was expected?

3.If you compiled the results for the whole class, what results would you expect?

4.How do the expected results differ from the observed results?

C. Segregation

• Mendel wondered if the recessive alleles had disappeared or were they still present in the F1 plants .He allowed all 7 kinds of F1 hybrids to produce an F2 generation by self-pollination

• F1 cross-recessive traits reappeared(~ ¼ F2 showed recessive trait)

• Mendel said the alleles for tall and short segregated(separated) during formation of sex cells

• Each gamete (Sex cell) carries a single copy of each gene

• F1 produces 2 types of gametes-one has short allele and one has tall allele.

• ______________letter stands for dominant allele and lower case letter for __________________.example:Tt T stands for tall and lower case for short.

big recessive

Probability and Punnett Squares

– Likelihood for occurrence for a particular event is __________________________

– PAST OUTCOMES DO NOT AFFECT FUTURE OUTCOMES

– Probability is used to determine genetic occurrences using a diagram called a ___________________-which can predict and compare genetic variations that will result from a cross.

probability

Punnett square

– ____________________means the organism has the same 2 alleles for a trait---TT—also called true-breeding

– _______________means the organism has 2 different alleles for a certain trait---Tt-also called hybrid.

– ______________is the observed physical trait----example:tallness or shortness

– ________________=genetic makeup or actual alleles----example:TT or Tt

homozygous

heterozygous

phenotype

genotype

Section 11-2Tt X Tt Cross

Section 11-2

Tt X Tt Cross

Tt

T t

TT Tt

tT tt

Genotypes:___TT__Tt_____tt Phenotypes:____tall _____short

1 21

3

1

– Each offspring will have the same probability of a genotype and phenotype because each is ____________or a single occurrence

– Larger the # of offspring ,the closer to_________________

–predicted ratio.

segregated

III.Mendelian Genetics 

• Mendel wondered if the segregation of one pr of alleles affected another(?)

• A) Independent Assortment– To answer his questions ,he performed a

______________.• 1)Two-Factor Cross F1

– Crossed truebreeders w/ only round yellow peas (genotype RRYY) x plants w/wrinkled green peas(rryy)

– Offspring were round yellow,establishing the dominance of RRYY

• Resulting genotype RrYy

2 factor cross experiment

ry ry ry ry

 RY RrYy RrYy RrYy RrYy

 RY RrYy RrYy RrYy RrYy

 RY RrYy RrYy RrYy RrYy

RY RrYy RrYy RrYy RrYy

rryy x RRYY

2) The Two factor Cross:F2

– All F1 plants were ______.He wanted to see how the alleles will segregate when F1’s are crossed w/ each other to make an F2 generation

– F2 produced 556 seeds-315 round 7 yellow and 32 were wrinkled and green

– ______seeds had a combination…Therefore seed shape separated separately from color.

– This is known as ______________________-genes segregate independently during formation of gametes.This accounts for much of the variation in color

Heterogeneous for seed shape and color 209

The Principle of Independent Assortment

B.Summary of Mendel’s Principles

• Inheritance of biological characteristics is controlled by genes from the parents

• When there are 2 or more alleles of a gene,then one is dominant and one is recessive

• Most sexually reproducing organisms have 2 adults w/ 2 copies of each gene-one from each parent.

• Alleles usually segregate independently.

C. Beyond Dominant and Recessive alleles

• Exceptions to the rules• Majority of genes have more than 2 alleles.• Some are neither dominant nor recessive and

multiple genes and alleles or genes control traits• 1 ) Incomplete dominance-one allele is not

completely dominant over another one

• 2) ____________-both alleles contribute to the phenotype—example –in chickens the allele for black feathers is codominant with white---this results in __________offspring

• 3) _______________-more than 2 possible alleles exist in a population(not in one organism-example-rabbits have 1 gene for coat color,but 4 possible alleles for that gene….also an example is genes for human blood type

• 4)_____________-traits controlled by 2 or more genes’ INTERACTION-4 different genes cover probably control human skin color

CODOMINANCE

SPECKLED

MULTIPLE ALLELES

POLYGENIC TRAITS

D.Applying Mendel’s principles

– _____________________started using fruit flies to study genetics-______________________________________They are easy to study because they produce many offspring quickly….Mendelian genetics applied to them

MORGAN

Drosophilia melanogaster

E. Genetics and the Environment

– Traits not determined solely by genes• Traits determined by

____________________________

Interaction of the genes and the environment they are in.

IV. MEIOSIS

• Mendel’s principles require 2 things-1)each organism inherits a single copy for every gene from each parent.

• When an organism produces its own gametes,those 2 sets of genes must be separated from each other so that each gamete has only 1 set

Chromosome #– The sets of chromosomes will be

homologous,meaning that one from male corresponds w/ one from female

– A cell w/ both sets of homologous chromosomes is _______________,meaning 2 sets(2N)---For Drosophilia,2N=8-2 complete sets of chromosomes and 2 complete sets of genes.

– Gametes,however contain a __________________#-1 set of chromosomes-for Drosophilia N=4.

diploidhaploid

• B. Meiosis=_______________________________________________________________________________________________

Process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell

• 2 divisions-Meiosis I and Meiosis II

Meiosis I –

• Chromosomes are replicated 1st• Divide similar to mitosis,except in prophase I

each chromosome pairs w/ its corresponding chromosome to make a __________________-which has 4 chromatids

• They exchange portions of their chromatids in _______________________-resulting in a exchange of alleles between homologous chromosomes and produces new combinations of alleles.

• Homomlogous chromosomes separate and 2 new cells are formed

• Each cell has 4 chromatids,but they are separated

tetrad

Crossing-over

Meiosis II-

• No replication(of chromosomes) previous to Meiosis II-unlike w/ meiosis I

• Each chromosome has 2 chromatids• 4 daughter cells contain haploid # (N)

Go to Section:

Section 11-4

Figure 11-15 Meiosis

Meiosis I

Go to Section:

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis I I

• C. Gamete Formation-In female- 1 egg cell produced and 3 ______________________.

• Male produces 4 sperm cells• D. Comparing Mitosis and meiosis

– Mitosis produces 2 genetically alike diploid cells /also allows for growth

• Meiosis produces 4 genetically different haploid cells/for sexual reproduction

Polar bodies

V. Linkage and Gene Mapping

• A. Linkage– Morgan in 1910 discovered the principle of

linkage-certain genes inherited together• Drosophilia had 4 linkage groups----

CHROMOSOMES assort independently,not the genes

IV.Linkage & Gene Maps

• .Crossing –over during meiosis separates genes on the same chromosome onto homologous chromosomes---This gives great genetic ____________________.

diversity