Download Unit 6 Genetics - centralmountainbiology

Unit 6 Genetics
Module B: Continuity and Unity
of Life
Objectives:
1. Genes and inheritance
2. Mutations and chromosome
abnormalities
3. Genetic engineering
Lesson 1: Genes and Inheritance
• Gene – region of DNA that codes for a
specific protein.
• Allele – different versions of a gene
• Polygenic – trait that is determined by
more than one gene.
Dominant and Recessive Alleles
• Phenotype: physical appearance of a
trait. (physical appearance)
• Genotype: the alleles of a trait.
(genetic makeup)
• Dominant allele – when present it is
expressed.
• Recessive allele – masked if a
dominant allele is present.
• Dominant and Recessive Alleles
• Pea plants inherit two alleles for traits.
– Tall is dominant “T”
– Short is recessive “t”
Pea plant’s possible genotypes for height:
Genotype
Phenotype
TT (homozygous dominant)
tall
Tt (heterozygous dominant)
tall
tt (homozygous recessive)
short
Homozygous: when there are two of the
same alleles for a trait.
Ex. TT, tt
Heterozygous: when there are two
different alleles for a trait.
Ex. Tt
Identify the following:
Tt
Answer: genotype, heterozygous
Tall
Answer: phenotype
Homozygous recessive
Answer: genotype
• Punnett Squares
- Shows the possible allele combinations
and phenotypes of the offspring of a
given set of parents.
A = dominant yellow
a = recessive green
Probability:
Yellow =
Green =
Ratio =
• Pedigree chart – can be used to trace
inheritance of a trait through multiple
generations of related individuals.
• Males = squares
• Females = circles
• Shaded shapes indicate that person has
the trait. AA or aa
• Half-shaded shapes indicate that person
is a carrier, doesn’t express trait. Aa
• Horizontal bar connecting two individuals
represents a set of parents.
• Vertical bar represents offspring.
Incomplete
Dominance, CoDominance, and
Multiple Alleles
- Incomplete
dominance –
heterozygous
individual has a
phenotype that
differs from those
with either
homozygous
genotype.
- Blending of two
alleles.
Co-dominance – heterozygotes express
both the dominant and recessive
phenotypes, rather than a blend.
-expresses both traits.
Ex. Roan cattle
• Multiple-allele – some genes have
more than two possible alleles.
• Ex. ABO blood type
Alleles: IA, IB, i (i is O type)
• Blood type is determined by the
presence of a carbohydrate group
attached to a protein on the surface
of red blood cells.
Sex-linked traits
• Traits found on the genes on a sex
chromosome.
• Sex chromosomes are XX female or XY
male.
• X chromosome is larger and contains
more genes than the Y.
• Ex. Hemophilia – blood-clotting disorder is
determined by a single gene on the X
chromosome.
• The allele is recessive, males get it more
because they only have one X
chromosome.
• A man with hemophilia and a woman
who has no history of the disease in her
family plan to have a child. The
parents’ genotypes are XhY and XHXH
• Homework: pg. 138 – 140
• Questions 1-6
• Due Wednesday