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BIOLOGY (Chapter 15 - Genotypes & phenotypes (Genotype (An…
BIOLOGY
Chapter 15 - Genotypes & phenotypes
Cystic Fibrosis
CFTR gene (chromosome 7), responsible for production of a transporter protein
C = normal transporter protein production, c = defective
Phenotype
Expression of an organism's genetic makeup (genes) that is
visible, measurable
and
detectable
Expression
Structural, functional, biochemical and physiological
Can be as a
single feature
of a
structure/function of an organism
(e.g. colour of petals) or
multiple feature
(e.g. CF gene - abnormal mucus production)
E.g. colour of fruits, blood types, bacteria resistance to antibiotics
Visible phenotype caused by:
a single gene which causes a particular physical or physiological expression
interaction between multiple genes at two or more loci
Genotype
An organism's genetic makeup at a particular gene locus that determines its phenotype and is not visible, only its effects can be seen and measured
Homozygous:
the two alleles of a gene are identical e.g. CC or cc
Heterozygous:
the two alleles of a gene are different e.g. Cc
Genes and their traits described by chromosomal location:
autosomal, X-linked, Y-linked
When an
autosome
has
two alleles for a gene
, the max number of different genotypes is
3
Traits controlled by alleles located on the sex chromosomes do not appear equally in both sexes
Genes on Y chromosome
- small segments of DNA at each ends are homologous with DNA segments on the X chromosomes
SRY Gene
Swyer Syndrome 46 XY
Inactive SRY gene - no testis formation
Rare XY female
At birth, external characteristics of a normal female
No ovaries, has traces of gonadal tissue (streak gonads)
Deletion of part/all of this gene results in
azoospermia
- no sperm in semen
Relationship between expression of alleles
Dominant/Recessive (complete dominance)
Co-dominance
The two alleles of a gene are expressed in an organism's heterozygote phenotype e.g. blood types (like AB, which is a mix of A and B)
Some cases,
genotype + environment = phenotype
E.g. Siamese cats, which develop pigment in certain areas due to tryosinase, which is heat-senstive (pigmentation appears on coolest parts of cat's body)
Polygenic inheritance
Epigenetics
Chapter 16 - Genetic crosses: Rules of the game
Punnet Square:
shows the chance of each possible outcome
Monohybrid cross:
a cross involving alleles of just one gene at a time. Involved the segregation of alleles of the same gene into separate gametes.
When explaining results of a monohybrid cross:
genotype
- homozygous dominant: heterozygous: homozygous recessive
phenotype
- dominant: recessive
Monohybrid crosses of autosomal genes:
expected results from
2 heterozygote parents
is a
3:1 ratio of offspring
showing the dominant phenotype to those showing the recessive trait
Variation only occurs when the relationship between the alleles in co-dominant or when one of the alleles is lethal in the homozygous condition
Chapter 9 - Cell cycle
Prokaryotic and eukaryotic cells
Why cells replicate
The cell cycle
Binary fission
Mitosis
Chapter 10 - Asexual reproduction
Chapter 11 - Sexual reproduction
Chapter 12 - Cell growth & differentiation
Chapter 13 - Genomes, genes & alleles
Chapter 14 - Chromosomes: the carriers of genes