Biology : Ch. 8 : Mendel and Heredity - PowerPoint PPT Presentation

1 / 36
About This Presentation
Title:

Biology : Ch. 8 : Mendel and Heredity

Description:

Genetics is defined as the study of heredity. ... After studying genetics for 30 years Mendel concluded that each organism has two ... – PowerPoint PPT presentation

Number of Views:159
Avg rating:3.0/5.0
Slides: 37
Provided by: dayto1
Category:

less

Transcript and Presenter's Notes

Title: Biology : Ch. 8 : Mendel and Heredity


1
Biology Ch. 8 Mendel and Heredity
  • In this chapter we will focus on the work of
    Gregor Mendel, which has led to our modern
    understanding of genetics.
  • Genetics is defined as the study of heredity.
  • Heredity is the passing on of characteristics
    from parents to offspring.

2
Mendels Laws of Heredity
  • Gregor Mendel (1843) was an Austrian Monk who
    studied the reproduction of garden pea plants.
  • The pea plant reproduces sexually, meaning that
    two distinct sex cells (gametes) meet to form an
    offspring.
  • In the pea (as in other plants) the pollen is the
    male gamete, and the ovule is the female gamete.

3
Mendels Laws of Heredity
  • The pollen from the male part of the pea plant
    (anther) falls on the ovule from the female part
    of the plant (pistil), and fertilization occurs.
  • Pollination refers to the pollen meeting the
    ovule of plants.
  • Pollination can be self pollination or cross
    pollination.

4
Mendels Laws of Heredity
  • To study the offspring of the garden pea plants
    Mendel had to carefully transfer pollen from one
    plant to another plant. This is called making a
    cross.
  • By careful research Mendel was able to control
    which plants were fertilized by which plant, and
    was able to make some conclusions about the
    passing down of traits or characteristics from
    parents to offspring.

5
Mendels Crosses
  • Mendel gave the following symbols to describe the
    study of heredity or genetics in crosses
  • P parents
  • F1 first filial generation
  • F2 second filial generation

6
Mendels Crosses
  • Mendel first cross involved studying one trait.
    (height). This is called a monohybrid cross
    since only one trait is studied from the parents
    to the offspring.
  • He crossed a tall pea plant with a short pea
    plant, and found all the(F1) offspring were tall.
  • He then crossed the F1with each other and found 1
    in 4 of their offspring was short.

7
Mendels Monohybrid Cross Pea Plant Height
8
Mendels Conclusions
  • After studying genetics for 30 years Mendel
    concluded that each organism has two factors for
    each of its traits. These different gene forms
    are called alleles.
  • Mendel also concluded that alleles can be
    dominant or recessive. The dominant allele seems
    to cover up the recessive allele for a given
    trait.

9
End of Section 1
10
Representation of Alleles
  • Alleles, which are a form of a gene are
    represented by capital or lower case letters, to
    show the dominant or recessive allele of each
    trait.
  • For pea plant height T dominant allele for
    tall plants, t recessive allele for short
    plants.
  • A pea plant with Tt tall
  • A pea plant with TT tall
  • A pea plant with tt short

11
Mendels Law of Segregation
  • Mendel concluded that the two alleles for for
    each trait must separate when gametes are formed.
    A parent passes on at random one of its alleles
    for each trait.

12
Trait Terminology
  • Many traits which are passed on are controlled by
    two alleles. The following are the names for the
    types of alleles for each trait
  • TT homozygous dominant
  • Tt heterozygous
  • tt homozygous recessive
  • The way a trait is expressed or how an organism
    appear is the phenotype (TT tall, Tt tall)
  • The actual alleles for a trait is the genotype.
    (TT,Tt,tt)

13
Mendels Dihybrid Crosses
  • A dihybrid cross involves studying two traits at
    the same time.
  • When Mendel studied the color of the pea seed and
    the shape of the seed (wrinkled, or round), he
    found that different traits are inherited
    independently of each other. This is called the
    law of independent assortment.
  • Today this law is true only if the alleles for a
    trait are located on a different chromosome.
    Some traits are not independently assorted to the
    offspring. Some traits are more packaged due
    to meiosis.

14
Punnett Squares
  • Punnett Squares are used to predict the
    offspring of a cross.
  • A punnett square uses the male gamete on the top,
    the female gamete on the side, and possibilities
    of the offspring in the boxes.
  • A punnett square will give you a predicted
    phenotypic and genotypical ratios of offspring.

15
Punnett Squares
RRYy
  • Dihybrid Crosses A dihybrid cross involves the
    study of two traits passed on to offspring.
  • A dihybrid cross requires a 4 x 4 box to
    calculate.
  • Possible alleles for the male and female are
    noted on the outside.

RRYy
16
Example Dihybrid Cross
Traits B black coat b red coat , T
tall , t short What is the predicted offspring
of a heterozygous black coat bull which is
heterozygous for tall and a heterozygous black
coat cow which is heterozygous for tall?
BbTt
BT
Bt
bT
bt
BT
Bt
BbTt
bT
bt
17
Inheritance of Traits
  • Traits are inherited on the autosomes or sex
    chromosomes.
  • If a gene for a trait is located on the sex
    chromosome the trait is termed sex-linked
  • Examples baldness, color blindness, hemophilia

18
Pedigree
  • A pedigree is a chart used to study inheritance
    of traits.
  • A pedigree is a family history diagram.

19
Pedigree
  • A pedigree uses circles to represent females, and
    squares to represent males.
  • The allele to be studied is represented by
    shading of the circles and squares.
  • A pedigree consists of different generations of
    the individual

20
Inheritance Patterns
  • Mendelian inheritance dominant and recessive
    alleles. The dominant allele covers the
    recessive allele.
  • Individuals who are heterozygous are termed
    carriers of the recessive allele.

Tongue rolling explained by mendelian
inheritance
21
Inheritance Patterns
  • Incomplete dominance
  • The mixing of alleles to provide a trait.
    Heterozygous genotype is an intermediate between
    the two alleles.
  • Red flower x White flower pink flower.

22
Inheritance Patterns
  • Codominance pattern of inheritance in which
    different alleles may dominate different areas of
    an organism.
  • Ex calico cats, cattle, speckled chickens,
    baldness patterns, etc.

23
Inheritance Patterns
  • Polygenic complex traits which are a result of
    many genes.
  • Ex. Eye color, height, weight, skin color, etc.

24
Inheritance Patterns
  • Multiple alleles inheritance pattern involving
    three or more alleles to determine a trait.
  • Ex. Blood type

25
Blood Types Multiple Alleles
  • Human blood types are determined by proteins
    found on the Red Blood Cells.(Antigens)
  • Possible alleles
  • IA - protein A
  • IB - protein B
  • I no surface proteins

26
Blood Types
  • Human Blood Type is determined by one allele from
    the mother and one allele from the father. The
    alleles show codominance.

27
Blood Types
  • Blood antigens(proteins) are important to
    identify when donating and receiving blood.
    Different proteins will bond with other proteins
    and cause clotting or coagulation of the blood.

28
Blood Types
  • Blood Types
  • O universal donor
  • AB universal acceptor

29
Rh Factor
  • Another protein may be present on the RBCs. This
    protein is called the Rh factor.
  • If a mother is Rh- and a developing baby is Rh
    the mother will build up anti Rh proteins
  • The mothers second child, if Rh will have
    complications due to the mothers antibodies
    fighting the Rh proteins of the child

30
Environmental Influence
  • A phenotype of an individual is also linked to
    their environment.
  • Example Arctic fox in the winter white coat,
    Arctic fox in summer darker coat.

31
Genetic Disorders
  • Sickle Cell Anemia
  • Autosomal recessive trait
  • Red Blood Cells lack proper shape to carry oxygen
    and carbon dioxide to and from cells

32
Cystic Fibrosis
  • 1 in 2000 children are born with CF.
  • To be born with CF you need both recessive
    alleles.
  • CF alleles cause thick mucus in the lungs and
    respiratory tract

33
Hemophilia
  • Hemophilia is a sex-linked trait. A hemophiliac
    lacks the ability for blood to clot.
  • Most hemophiliacs are male. (one allele)
  • A recessive sex-linked disorder.

34
Huntingtons Disease
  • Lethal disorder caused by a dominant allele.
  • Results in a degeneration of the nervous system
  • Generally is expressed at age 30 50

Dominant allele
35
Tay Sachs Disease
  • Autosomal Recessive disorder
  • Lack of an enzyme which breaks down a lipid. The
    lipid builds up in tissue.
  • Blindness, loss of movement, and mental
    deterioration.

36
Treating Genetic Disorders
  • Gene therapy involves trying to isolate and
    replace certain genes in cells.
  • Viruses have been used to transfer genes into
    cells to alter the desired gene.
  • Viruses however are naturally attacked by the
    immune system.
Write a Comment
User Comments (0)
About PowerShow.com