Heredity

1
Heredity

• LN 18

California Content Standard Genetics 2g. Students
know how to predict possible combinations of
alleles in a zygote from the genetic makeup of
the parents.
2
What is Meiosis?

• Meiosis makes SEX CELLS.
• Haploid cells
• Gametes
• Sperm egg cells
• Diploid is 2n
• All of our body cells are diploid.
• Haploid is n
• ONLY gametes are haploid.

fertilization


3
What is a Phenotype?
Phenotype widows peak

• A phenotype describes what an organism looks
  like.
• In order to determine an organisms phenotype you
  need to look at it.

Phenotype free earlobes
Phenotype attached earlobes
4
What is a Genotype?
Gene location for earlobes.

• A genotype is the combination of genes in an
  organism.
• Genes are section of DNA that codes for a trait.
  Genes are located on chromosomes.
• Alleles are different forms of a gene.
• Genes are labeled by using letters.

F free
f attached
F and f are alleles.
Genotype Ff
Homologous chromosomes have genes for the same
trait.
5
Who was Gregor Mendel?

• Mendel carried out the first important studies in
  heredity.
• Mendel studied heredity using pea plants.
• Mendel was the first to develop laws and rules
  for heredity.
• One of Mendels rules is the rule of dominance.
• Some traits are dominant and others are recessive.

(1822 1884)
6
Punnett Squares

• Punnett squares are used to determine the chance
  of seeing a trait in the offspring.
• Remember every organism has two copies of a gene.
  Only one of the two is passed to the offspring.
  
• If the genotype of a father is Aa, then he can
  either pass down A or a.

7
Words to know

• Monohybrid cross involves studying a single
  trait.
• Homozygous means that both alleles are the same.
  We can have homozygous dominant, TT or homozygous
  recessive tt.
• Heterozygous means that the alleles are different
  from one another. We would have Tt.
• With the rule of dominance TT and Tt have the
  same phenotype. The only way to show a recessive
  trait is to be homozygous recessive, tt.

8
Monohybrid Cross problem

• Widows peak is a dominant trait (P).
• A woman homozygous dominant for widows peak
  marries a man without a widows peak. What are
  the chances that their children will have a
  widows peak?

Parents genotype
PP x pp
P P
p p
Pp
Pp
Pp
Pp
100 chance that the children will have a widows
peak.
9
Summary

• What is a genotype and phenotype?
• Who was Mendel?
• What are Punnett squares used for?
• What are alleles?
• How are homozygous and heterozygous different?