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Biology

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Biology Genetics Unit Gregor Mendel Considered the father of modern genetics He was an Austrian monk in the mid 1800 s He did many experiments with pea plants ... – PowerPoint PPT presentation

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Title: Biology


1
Biology
  • Genetics Unit

2
Gregor Mendel
  • Considered the father of modern genetics
  • He was an Austrian monk in the mid 1800s
  • He did many experiments with pea plants

3
Mendel Continued
  • He discovered the basics for genetics as we know
    it today
  • In the following slides, we will cover his major
    discoveries

4
Dominant Traits
  • In a pair of traits, this one always has an
    effect
  • These traits get represented with a capital
    letter (B)

5
Recessive Traits
  • A trait that is only seen when two copies of the
    gene are present

6
Alleles
  • Different forms of the same trait or gene
  • Examples would be blue and brown eyes, or
    hitchhikers and straight thumbs

7
Homozygous
  • A term describing an organism that has two of the
    same genes
  • This could be two dominant traits (BB) or two
    recessive traits (bb)

8
Heterozygous
  • A term describing organisms that have two
    different genes for a trait.
  • This means they have one dominant and one
    recessive trait (Bb)

9
Genotype
  • The genes that an organism has for a trait.
  • For example, attached earlobes are a recessive
    trait, so a person with them must have two copies
    of that trait.
  • Therefore, their genotype is ee.

10
Phenotype
  • This is the actual, physical trait that a person
    has.
  • For example, if a person has the genes Ee for
    earlobe shape, their phenotype will be the
    dominant trait, which is free earlobes.

11
Incomplete Dominance
  • Sometimes, one trait does not dominate the other,
    and both the dominant and recessive traits are
    seen.

12
Codominance
  • With some traits, there can be more than one
    dominant allele.
  • A good example is blood type. Type O is
    recessive, but types A and B are both dominant.

13
Punnett Squares
  • Punnett Squares are charts that are made in order
    to predict the results of two organisms
    reproducing.
  • Usually only one or two traits are analyzed at a
    time.

14
Single Trait Punnett Square
  • The Problem Brown eyes are dominant and blue
    eyes are recessive. Cross a heterozygous woman
    with a homozygous recessive male.
  • Step 1 define letters to represent the traits
  • B brown b blue
  • Step 2 write down Mom and Dads genotypes
  • Mom Dad
  • Bb bb

15
Single Trait Punnett Square
  • Now make the chart and put Mom and Dads genes on
    the chart.

16
Single Trait Punnett Square
  • Now, bring the genes across and down to determine
    the genes the possible offspring will have.

17
Two Trait Punnett Square
  • In this problem we will look at two traits at the
    same time.
  • Problem make a Punnett Square using the
    following combinations of genes.
  • Mom Dad
  • AaBb AABb

18
Two Trait Punnett Square
  • Now, find the combinations of genes Mom and Dad
    can pass on.
  • Mom - AaBb Dad - AABb
  • AB AB
  • Ab Ab
  • aB AB
  • ab Ab

19
Two Trait Punnett Squares
  • Now, take those traits and put them on a chart.

20
Two Trait Punnett Squares
  • Finally, fill in the boxes.

21
Sex-Linked Punnett Squares
  • These are traits that are only found on the X
    chromosome.
  • Females have XX and males have XY
  • The X chromosome is very large and the Y is very
    small. Because of this, there is not enough room
    on the Y for all of the genes on the X.

22
Sex-Linked Punnett Squares
  • The Problem Color blindness is a sex-linked
    recessive trait. Normal vision is dominant.
    Cross a heterozygous woman with a man who has
    normal vision.
  • Step 1 assign letters to the trait
  • B normal b color blind

23
Sex-Linked Punnett Squares
  • Step 2 add genes to Mom and Dads X chromosomes
  • Mom Dad
  • XBXb XBY

24
Sex-Linked Punnett Squares
  • Now, add Mom and Dads genes to the chart.

25
Sex-Linked Punnett Squares
  • Finally, fill in the squares on the chart.

26
Pedigree Charts
  • Pedigrees show the occurrence of specific genetic
    traits in a family.
  • Each generation is designated by a Roman numeral
  • Females are circles and males are squares
  • When possible, the oldest person in a generation
    goes on the left. As you go to the right, the
    people should get younger.

27
Pedigree Charts
  • In the chart below, the man and woman are
    connected by a horizontal line. This means they
    are married.

28
Pedigree Charts
  • The vertical line dropping from the marriage line
    indicates children being born.

29
Pedigree Charts
  • Marriages in generation II are shown below. A
    first marriage is always shown to the left, the
    second to the right.

30
Pedigree Charts
  • Children are then added and generation III is
    formed. Note how twins are shown.

31
Pedigree Charts
  • People with the recessive trait are shaded and a
    key is added to explain the traits.

32
Pedigree Charts
  • Finally, genotypes are added to the chart.
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