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Flashcards in The Principles of Inheritance Deck (12)
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1

TRAITS AND GENES

- A trait is an inherited characteristic of an individual (many traits are each the result of a single gene)
- Since a trait may have varieties (e.g. curly vs straight hair) it must be possible for their to be carriers of the same gene (this individual genes can have multiple forms; alleles)
- Alleles differ in DNA sequence in small ways
- Potentially this results in proteins that differ somewhat in amino acid sequence and that may lead to differences in the activity of the proteins

2

INHERITANCE OF TRAITS

- So the basis of differences between individuals is due to there being alleles
- The genotype of the offspring is made up of all pairs of alleles inherited from its parents
- The set of genes for any organism are present in strands of DNA called chromosomes
- Thus: the genome of each organisms comprises pairs of chromosomes
- Each particular gene for a particular species is always in the same location on the same chromosome in each member of the species

3

PRINCIPLES OF SEGREGATION

- Individuals carry pairs of alleles that influence particular traits
- The alleles segregate during the formation of gametes (sperm and ova) such that any individual gamete contains only one of each pair of alleles
- Gametes are formed through a special form of cell division called meiosis

4

MEIOSIS

- Meiosis is unique to the production of sperm and ova
- The parent cell has pairs of chromosomes just like all the other cells in the body

5

SIMPLIFIED MODEL LOOKING AT THE FATE OF JUST ONE PAIR OF CHROMOSOMES

- The first thing that happens is an exact duplicate of each chromosome is made
- The parent cell undergoes cell division to produce up to 4 gametes
- Each gamete will only have one chromosome from each pair

6

ALLELES AND EXPRESSION

If someone is homozygous for a particular gene
- The alleles of the gene are the same
- The cells of that person will produce one version of the protein encoded by the gene

If someone is heterozygous for a particular gene
- The alleles are not identical
- The cell;s of that person may produce 2 versions of the protein encoded by the gene
- But this is not always the case

- The genotype of a person is made up all of pairs of alleles inherited from its parents
- The phenotype of a person is the collection of traits of that person
- These are the result interactions between the alleles

7

PATTERNS OF INTERACTION BETWEEN ALLELES: CO-DOMINANCE

In case of co-dominance, in the heterozygote, both alleles are expressed equally

8

PATTERNS OF INTERACTION BETWEEN ALLELES: INCOMPLETE DOMINANCE

In incomplete dominance, the phenotype of heterozygote lies between each of the homozygotes

9

PEDIGREES: AUTOSOMAL AND X-LINKED

Autosomal chromosomes are chromosomes 1-22
Sex chromosomes are the 23rd pair

10

AUTOSOMAL DOMINANT INHERITANCE

- Both genders exhibit the trait in approximately equal numbers
- Disease should not skip generations

11

X-LINKED RECESSIVE INHERITANCE

- Trait more frequently seen in males
- Not transmitted from father to son
- Disease can skip generations
- Female carriers will transmit it to approximately half their sons

12

AUTOSOMAL RECESSIVE INHERITANCE

- Both genders exhibit the trait in approximately equal numbers
- Disease may skip a generation
- If carriers mate: approximately one quarter of offspring will be affected