understanding heredity

36
UNDERSTANDING HEREDITY Part 1 1 1

Upload: gagan

Post on 23-Feb-2016

27 views

Category:

Documents


0 download

DESCRIPTION

Understanding Heredity. Part 1. 1. The work of gregor mendel. The Work of Gregor Mendel. ALL living things have a set of characteristics that are contained in genes. These genes come from our parents and are found in every cell in our body. Genetics – the scientific study of heredity. - PowerPoint PPT Presentation

TRANSCRIPT

Page 1: Understanding  Heredity

UNDERSTANDING HEREDITYPart 1

1

1

Page 2: Understanding  Heredity

THE WORK OF GREGOR MENDEL

2

Page 3: Understanding  Heredity

The Work of Gregor Mendel•ALL living things have a set of characteristics that are contained in genes.

•These genes come from our parents and are found in every cell in our body.

•Genetics – the scientific study of heredity

3

Page 4: Understanding  Heredity

The Work of Gregor Mendel, cont.•Gregor Mendel – an Austrian Monk born in 1822

•He laid the foundation for much of our understanding of inheritance patterns

•Credited as the “Father of Genetics”

4

Page 5: Understanding  Heredity

The Work of Gregor Mendel, cont.5

•He was a mathematician/botanist and was in charge of the monastery garden

•He noticed that individual plants of the same species were not identical

Page 6: Understanding  Heredity

The Work of Gregor Mendel, cont.• He wanted to know why they were not identical, so he experimented on pea plants to help answer the question.

6

Page 7: Understanding  Heredity

The Work of Gregor Mendel, cont.

•He selected seven traits found in pea plants to study:

1. Seed shape2. Seed color3. Pod shape4. Pod color5. Plant height6. Flower color7. Flower position

7

Page 8: Understanding  Heredity

8

Page 9: Understanding  Heredity

The Work of Gregor Mendel, cont.Why pea plants?1. Pea plants are pure breeding –

they produce identical offspring when they self-pollinate

2. They grow fast3. They have traits in distinct

alternate forms (either/or)

9

Page 10: Understanding  Heredity

The Work of Gregor Mendel, cont.•These characteristics allowed Mendel to control the outcome when he cross-pollinated plants with contrasting traits

•The resulting offspring are called a monohybrid cross

10

Page 11: Understanding  Heredity

The Work of Gregor Mendel, cont.How did he make these monohybrid crosses?1. Mendel prevented self-

pollination in the plants by removing the stamen

2. He dusted the pollen from one stamen onto another plant’s pistil (cross polination)

3. The result: cross-breed plants

11

Page 12: Understanding  Heredity

12

Page 13: Understanding  Heredity

The Work of Gregor Mendel, cont.What happened next?•He called the original plants the Parent (P) generation

•The offspring produced by the P generation were the F1 generation; also called hybrids

13

Page 14: Understanding  Heredity

The Work of Gregor Mendel, cont.•All of the hybrids showed the traits of only one of their parents…

•The traits from the other parent had disappeared!

14

Page 15: Understanding  Heredity

The Work of Gregor Mendel, cont.Where did those traits go?•To answer that question, Mendel let the F1 plants self-pollinate

•This produced the F2 generation: ~ ¾ of the plants showed the traits of their parents (the F1 generation) ~ ¼ of the plants showed the traits of their grandparents (the P generation)

15

Page 16: Understanding  Heredity

The Work of Gregor Mendel, cont.• This lead Mendel to make two conclusions about what he called biological inheritance (we call it genes):

1. Traits are passed from one generation to the next

2. Each trait is found in at least 2 contrasting forms

16

Page 17: Understanding  Heredity

The Work of Gregor Mendel, cont.• He further concluded that:a. Traits are inherited as distinct units from the

parentb. Organisms inherit 2 copies of each unit (one

per parent)c. Organisms donate one of those copies when

they make gametesd. The 2 copies separate (segregate) during

gamete formation• These conclusions became know as the Law of Segregation

17

Page 18: Understanding  Heredity

MODERN GENETICS

18

Page 19: Understanding  Heredity

Modern Genetics• Some traits are dominant over other traits

• The unit that seems to disappear is recessive – it can only be expressed when 2 recessive traits combine

19

Page 20: Understanding  Heredity

Modern Genetics, cont.• We refer to traits as genes• Genes are sections of chromosomes• Each form of the gene is called an allele

• An organism can be:Homozygous – having 2 identical alleles ORHeterozygous – having 2 different alleles

20

Page 21: Understanding  Heredity

Modern Genetics, cont.• Phenotype – the physical characteristics of the organism (what it looks like)

• Genotype – the genetic makeup of the organism (what is actually there)

The phenotype of an organism is the result of:1. The Genotype2. Environmental pressures

21

Page 22: Understanding  Heredity

PROBABILITY AND PUNNETT SQUARES

22

Page 23: Understanding  Heredity

Probabilities• Mendel realized that the Principle of Probability (the likeliness that a particular event will occur) could be used to predict and explain the results of genetic crosses.

• If there are 2 possible outcomes, then there is a 1 in 2 or 50% chance of each outcome occurring.

23

Page 24: Understanding  Heredity

Probabilities, cont.• Example: If you flip a coin 3 times in a row, what are the chances it will be heads up every time?

½ x ½ x ½ = 1/8

• Probabilities can predict the average outcome of a large number of events – not the outcome of an individual event.

• For that, we need Punnett Squares…

24

Page 25: Understanding  Heredity

Punnett Squares• The gene combination that might result from a genetic cross can be predicted and compared with a Punnett Square

• The dominant allele is represented by a capital letter (like T for tall)

• The recessive allele is represented by a lower case letter for the same trait (like t for short)

25

Page 26: Understanding  Heredity

Punnett Squares, cont.26

Page 27: Understanding  Heredity

Punnett Squares, cont.•Monohybrid cross - cross involving a single trait

ex. flower color

•Dihybrid cross - cross involving two traits

ex. flower color & plant height

27

Page 28: Understanding  Heredity

28

Page 29: Understanding  Heredity

NON-MENDELIAN GENETICS

Beyond Dominant & Recessive Alleles

29

Page 30: Understanding  Heredity

Beyond Dominant & Recessive Alleles

• Principle of Independent Assortment: genes for different traits can segregate independently during the formation of gametes

• This accounts for the genetic variations among organisms of the same species!

30

Page 31: Understanding  Heredity

Beyond Dominant & Recessive Alleles, cont.• The majority of genes have more than two alleles

• Many traits are controlled by more than one gene

• Most of the genes that affect the physical appearance of an organism are found on the autosomes

31

Page 32: Understanding  Heredity

Beyond Dominant & Recessive Alleles, cont.1. Incomplete dominance – case where one allele is not completely dominant over another; produces an intermediate type

32

Page 33: Understanding  Heredity

Beyond Dominant & Recessive Alleles, cont.

2. Codominance – both alleles contribute to the phenotype; it is a blend of the two alleles

33

Page 34: Understanding  Heredity

Beyond Dominant & Recessive Alleles, cont. 3. Multiple Alleles – one individual can only have two alleles but more than two alleles can exist in a population.

34

Page 35: Understanding  Heredity

Beyond Dominant & Recessive Alleles, cont.

4. Polygenic traits – many traits are produced by the interaction of several genes

Examples: hair, eye and skin color

35

Page 36: Understanding  Heredity

Beyond Dominant & Recessive Alleles, cont.5. The characteristics of an organism are also determined by the environment it lives in

36