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Summary Genes and Environment Lecture Notes
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A summary of the Genes and Environment lectures
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Historical PerspectiveVesalius Harvey Linnaeus Darwin Galton
human anatomy discovered blood Systema naturae Evolution theory discovered a greater
circulation which which is the stating that humans number of extremely
opened the doors to taxonomic can change able individuals is
experimentation on classification of all found in families with
the phenomena of life known living things extremely able
individuals and is not
random
/ / / / the closer the family
relatedness the
higher the incidence
of extreme ability
/ / / / developed an
apparatus measuring
several types of
human capabilities
/ / / / he also introduced
the use of twins to
discover the nature vs
nurture debate
/ / / / now considered the
father of behavioural
genetics
Provisional hypothesis of pangenesis - the cells of the body throw off gemmules that multiply and
aggregate themselves into buds and sexual elements
Gemmules - thought to be the miniature replicas of the parent cells that were thrown off by each cell
throughout its course of development
- we now know this theory is wrong
Layarckian theory of use and disuse - acquired characteristics can be inherited; if a characteristic is
used, it will be maintained and developed, if not, it will vanish
- Darwin remained unsure of the source of variability for the most part
Variation - if one parent were tall and the other were short, the offspring would be average height
________________________________________________________________________________
Mendel’s Laws and Beyond
Huntington’s disease:
- shows a consistent pattern of heredity
- affected individuals have on parent with the disease
1
,- a family tree can visualise such a hereditary disease
- dominant alleles
- affects people after the reproductive years
- the children of affected parents know they have a 50%
chance of developing the disease
- gene for HD codes for a protein called hunting-tin
Phenylketonuria (PKU):
- mentally disabled patient with excess levels of phenylpyruvic acid in their urine due to a
disturbance in the metabolism of phenylalanine
Phenylalanine - one of the essential amino acids that serves
as a building block of proteins and it present in many foods
- parents are usually not affected
- the risk of siblings developing it is 25%
- if parents are genetically related, their siblings are likely
to have PKU
- recessive alleles
- the gene can be identified in the foetus so that the
parents can prevent retardation be=y serving low-phenylalanine diet to child
Mendel’s first law of segregation :
- concluded that there are two elements of heredity (now called alleles) for each trait in each
individual and these two elements separate during reproduction
- one of the elements can dominate the other
- a non-dominant element is only expressed if both elements are recessive
Alleles - alternative forms of the same gene
Genotype - an individual’s combination of alleles
Phenotype - observed traits
Fundamental issue of heredity - the extent to which differences in genotype account for differences
in phenotype
Gametes - egg or sperm-cells
- offspring will always inherit the recessive allele form the unaffected parent but they have a 50%
chance of inheriting the dominant gene from the affected parent
2
, Mendel’s second law of independent assortment:
- the inheritance of one gene is not affected by the inheritance of another gene
- if two traits are inherited independently, offspring of all four types would be found
1. Dominant for both genes
2. Dominant for one gene and
recessive for the other
3. Recessive for one gene and
dominant for other
4. Recessive for both genes
- violated when genes of two traits
are close together and on the same
chromosome
- if two traits are inherited together,
offspring of two types would be
found (linkage)
1. Dominate for both genes
2. Recessive for both genes
Recombination - occurs during
meiosis in the ovaries and testes,
where gametes are produced
- during meiosis, each chromosome
duplicates to form sister
chromatids
- theses sister chromatids may cross over one another
- each chromatid will be transmitted to a different gamete
- the distance between loci can be estimated by the number of recombinations per 100 games
Centimorgan (map unit) - distance between two loci
- if two loci are far apart, recombination will separate the two as often as if they were on different
chromosomes
Linkage analysis - refers to techniques that use information about violations of independent
assortment to identify the chromosomal location of a gene and wether it is linked to other genes
- once a gene is found, the DNA variation responsible for the disorder can be found and the
protein coded by the gene can be studied
- HD and PKU are single-gene disorders
3
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