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Chapter 11 Introduction to Genetics. Genetics The study of the inheritance of traits.

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Presentation on theme: "Chapter 11 Introduction to Genetics. Genetics The study of the inheritance of traits."— Presentation transcript:

1 Chapter 11 Introduction to Genetics

2 Genetics The study of the inheritance of traits.

3 Gregor Mendel’s Peas 1800’s Austrian Monk that detected patterns in the inherited traits of pea plants. Recognized as the “Father of Genetics” – the study of the inheritance of traits.

4 The Work of Gregor Mendel Mendel observed several traits in his true-breeding peas. Mendel crossed pea plants containing contrasting traits. His results were surprising.

5 P Generation F 1 Generation F 2 Generation TallShortTall Short Section 11-1 Principles of Dominance

6 P Generation F 1 Generation F 2 Generation TallShortTall Short Section 11-1 Principles of Dominance

7 P Generation F 1 Generation F 2 Generation TallShortTall Short Section 11-1 Principles of Dominance

8 The Work of Gregor Mendel Mendel decided “factors” that controlled traits were passed on from parent to offspring, and that some of these factors were dominant over others.

9 Genes and Alleles Genes – chemical factors on chromosomes that control traits. Alleles - different forms of a gene often producing contrasting traits.

10 Law of Dominance For a given trait, some alleles are dominant and others are recessive. When inherited together, the dominant allele will always be expressed over the recessive allele.

11 Seed Shape Flower Position Seed Coat Color Seed Color Pod Color Plant Height Pod Shape Round Wrinkled Round Yellow Green Gray White Smooth Constricted Green Yellow Axial Terminal Tall Short YellowGraySmoothGreenAxialTall Section 11-1 Figure 11-3 Mendel’s Seven F 1 Crosses on Pea Plants

12 Law of Segregation Alleles separate (segregate) from each other during the formation of sex cells (gametes). During fertilization, alleles are brought back together (recombination).

13 Probability What is the probability of getting tails when tossing a coin? What is the probability of getting tails after tossing the coin four times and getting heads each time? Each coin toss is random and represents an independent event. It has no influence over future tosses. Therefore, each toss always has a 1 in 2 (50%) chance of getting tails.

14 Probability The segregation and recombination of alleles is random, so probability can be used to predict the outcome of genetic crosses. Probability is the likelihood that a particular event will occur.

15 Punnett Squares Punnett squares use probability to predict the average results of a genetic cross.

16 Terminology Genotype – the alleles for a trait. Symbolized using letters. Dominant traits are capitalized; recessive are lower case. T = tall t = short Phenotype – the expression of the trait. Descriptive. Tall, short, round, wrinkled…

17 Terminology Pure genotypes are called homozygous. TT, tt Hybrid genotypes are called heterozygous. Tt The phenotype of a pure or hybrid trait looks the same. tall

18 Punnett Squares Parent genotypes go on the outside of the Punnett square. Offspring genotypes go on the inside. Each square represents a 25% chance of offspring having a particular genotype.

19 Punnett Squares For the following genetic crosses, use a Punnett square to predict the phenotypes of the offspring. 1. Tt x Tt 2. Tt x tt 3. Yy x YY 4. RR x rr

20 Independent Assortment Mendel followed the inheritance of several traits at a time. He concluded that factors (genes) were inherited independently of each other. He called this “independent assortment”. Ex: round peas could be yellow or green. Wrinkled peas could be yellow or green. Texture and color were inherited independently of each other.

21 Beyond Mendel…….. Not all traits follow Mendel’s laws of dominance, segregation and independent assortment.

22 Incomplete Dominance Some alleles are not completely dominant. Skin color and in flowers, petal color is determined by incomplete dominance, and the resulting color is a blend.

23 Codominance Some alleles are codominant; both are fully expredded at the same time. Human blood type and fur color is controlled by codominant alleles.

24 Multiple Alleles Many genes have more than two alleles controlling the trait, however, you can only inherit two of them: one from the mother and one from the father. Human blood type and rabbit coat color.

25 Polygenic Traits Often a trait is controlled by more than one gene. Eye color in fruit flies involves the interactions of three genes. Human skin color involves more than four genes.

26 Environmental Influences The expression of a trait is not determined solely by genetics. The environment can influence the expression of a gene. Skin color Plant height

27 Sexual Reproduction Human body cells have 46 chromosomes. During reproduction, an egg cell is fertilized by a sperm cell, and their chromosomes unite. In producing sex cells, what must be done to the number of chromosomes?

28 Meiosis Meiosis is the process by which sex cells are produced that contain half the normal number of chromosomes.

29 Chromosome Number Homologous chromosomes contain genes for the same traits (alleles). One is inherited from the mother and one from the father. Human body cells have 23 pairs of homologous chromosomes.

30 Chromosome Number Cells with pairs of homologous chromosomes are called diploid (2N) cells. Body cells contain pairs of homologous chromosomes. In humans, 2N = 46

31 Chromosome Number Cells with only one chromosome from each homologous pair are called haploid (1N) cells Sex cells (gametes) are haploid. In humans, 1N = 23

32 Meiosis Meiosis involves one replication of chromosomes and two divisions of chromosomes. This is how the number gets cut in half.

33 Forming gametes In a male, the four halpoid cells become sperm. In a female, the four haploid cells become one egg and two or three polar bodies.

34 Mitosis and meiosis comparison mitosismeiosis One divisionTwo divisions Produces two daughter cellsProduces four daughter cells Maintains chromosome numberReduces chromosome number by half Daughter cells are diploid (2N)Daughter cells are haploid (1N) No genetic variation in daughter cellsGenetic variation in daughter cells Used in asexual reproductionUsed in sexual reproduction

35 11-5 Linkage and Gene Maps

36 Independent Assortment Mendel observed that traits seemed to be inherited independent of each other. We now know that it is entire chromosomes that sort independent of each other.

37 Gene Linkage Genes located on the same chromosome tend to be inherited together. They are “linked”. Ex: in fruit flies, red eyes and miniature wings Ex: in humans, blonde hair and blue eyes

38 Crossing-Over During meiosis when homologous chromosomes pair up (synapsis) sister chromatids may cross-over each other, break and rejoin resulting in new gene linkages. This is known as “crossing-over”.

39 Section 11-4 Crossing-Over

40 Section 11-4 Crossing-Over

41 Section 11-4 Crossing-Over

42 Crossing-over during meiosis separates linked genes. The farther apart the linked genes, the greater the probability they will be separated by crossing-over.

43 Gene Maps The rate at which linked genes are separated can be used to create a gene map of a chromosome. The higher the recombination rate, the farther apart the two genes. In other words, they will assort independently more often than genes located close together.

44 Chromosome Maps part=A272


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