Heredity and Genetics

1
Heredity and Genetics

• IIB2b. Make predictions concerning inheritance
  based on Gregor Mendels laws of heredity.

2
Genetic Expression

• Genes?
• Alleles?
• Genotype?
• Punnett square?
• Phenotype?

3
Genes Alleles

• A gene is a specific portions of DNA, determine
  hereditary characteristics.
• An allele is an alternate form of a gene.
• Alleles for a particular gene may be
• Dominant meaning this trait will most likely
  express itself.
• Recessive meaning this trait will be masked by
  the dominant allele unless it is present with
  another recessive allele.

4
Genotypes

• An individual has two of each chromosome
  therefore he/she has at least two alleles for
  each trait. The alleles may be identical,
  Homozygous, or different, Heterozygous.
• For example, GG and gg represent homozygous
  genotypes and Gg represents the heterozygous
  genotype.

5
Phenotype

• The phenotype of an organism is simply the
  characteristics it will have.
• For example if G is green and g is yellow the
  following genotypes will result in the listed
  phenotypes if green is dominant and yellow is
  recessive.
• GG green
• Gg green
• gg yellow

6
Punnett Square

• The Punnett Square is used by geneticists to
  express the possible combinations for a certain
  trait an offspring may inherit from its parents.

7
Gene Segregation
8
Monohybrid Practice Problem

• Create a punnett square and give the genotypic
  and phenotypic results for the cross between a
  father (Cc) and mother (Cc). In this instance
  cute (C) is dominant and ugly (c) is recessive.

9
Incomplete Dominance

• In Caucasians, both the straight (S) and curly
  (C) hair traits are dominant. The heterozygous
  condition (CS) results in wavy hair. What will
  be the genotypic and phenotypic ratios for a
  cross between a homozygous straight-hair
  individual and a heterozygous individual?

10
Codominance

• In some instances, a cross between two
  true-breeding individuals may result in a
  combination of the two traits. For example, in
  Cocker Spaniels a blue roan (BW) colored dog is
  an oddity in which the dogs coat is a mixture of
  both black (B) and white (W). As a breeder, one
  can make twice as much money for a blue roan than
  for a solid colored dog. What two parents would
  be most likely to produce a blue roan? (Black
  BB and White WW)

11
Sex-linked

• Some traits are carried on the X chromosome so
  they are called sex-linked traits. For example,
  male-pattern baldness is a sex-linked disorder.
  A male experiencing male-pattern baldness has
  received (XB, Y) from his parents. While a male
  who is not experiencing male-pattern baldness has
  received (Xb, Y) from his parents. Which parent
  decides whether the male will be bald or not?
  ____________ What is the probability that XBXb
  and XBY parents will produce a normal male
  child?

12
Monohybrid Practice Problem

• What will be the resulting phenotypic and
  genotypic ratios of a cross between a homozygous
  dominant individual and a homozygous recessive
  individual considering inflated (I) pods are
  completely dominant over constricted pods (i)?

13
Monohybrid Practice Problem

• What will be the resulting phenotypic and
  genotypic ratios of a cross between two
  heterozygous individuals considering yellow (Y)
  seeds are completely dominant to green (y) seeds?

14
Monohybrid Practice Problem

• What will be the resulting phenotypic and
  genotypic ratios of a cross between a homozygous
  recessive individual and a heterozygous
  individual considering that the gene for smooth
  (S) seeds is completely dominant to wrinkled (s)
  seeds?

15
Monohybrid Practice Problem

• If there are two pea plants one with dominant
  colored seeds (yellow) and the other with
  recessive colored seeds (green), how can we
  determine the genotype of the yellow seeded pea
  plant?

16
Testcross

• In dogs, there is an hereditary deafness caused
  by a recessive gene, d. A kennel owner has a
  male dog that she wants to use for breeding
  purposes if possible. The dog can hear, so the
  owner knows his genotype is either DD or Dd. If
  the dogs genotype is Dd, the owner does not wish
  to use him for breeding so that the deafness gene
  will not be passed on. This can be tested by
  breeding the dog to a deaf female (dd). Draw the
  Punnett squares to illustrate these two possible
  crosses. In each case, what percentage/how many
  of the offspring would be expected to be hearing?
  deaf? How could you tell the genotype of this
  male dog? Also, using Punnett square(s), show how
  two hearing dogs could produce deaf offspring.

17
Monohybrid Cross

• In humans, brown eyes (B) are dominant over blue
  (b). A brown-eyed man marries a blue-eyed woman
  and they have three children, two of whom are
  brown-eyed and one of whom is blue-eyed. Draw the
  Punnett square that illustrates this marriage.
  What is the mans genotype? What are the
  genotypes of the children?

18
Sex-Linked Genes

• In humans, the genes for colorblindness and
  hemophilia are both located on the X chromosome
  with no corresponding gene on the Y. These are
  both recessive genes. If a man and a woman, both
  with normal vision, marry and have a colorblind
  son, draw the Punnett square that illustrates
  this. If the man dies and the woman remarries to
  a colorblind man, draw a Punnett square showing
  the type(s) of children that could be expected
  from this marriage. How many/what percentage of
  each could be expected?

19
Sex-Influenced Traits

• Baldness in humans is a dominant, sex-influenced
  trait. This gene is on the autosomes, not the sex
  chromosomes. A man who is BB or Bb will be bald
  and will be normal only if he is bb. A woman will
  only be bald if she is BB and normal if she is Bb
  or bb (its almost like B is dominant in males
  and b is dominant in females). If two parents are
  heterozygous for baldness, what are the chances
  of their children being bald? Use a Punnett
  square to illustrate this. Note because the sex
  of a person does make a difference in how the
  gene is expressed, you need to set this up as a
  dihybrid cross to account for the sex of the
  children.

20
Dihybrid Crosses

• If the owner of a blue roan Cocker Spaniel (BW)
  knows that this dog is also heterozygous for ear
  length (Ll) and crosses (mates) him with a
  heterozygous female, what will be the phenotypic
  and genotypic results of this mating?