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MindMap Gallery Mendelian Genetics - Heredity Part II
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Mendelian Genetics - Heredity Part II
This Mind Map covers an important topic in Mendelian Genetics, that is, heredity. It describes the process of how a child receives genetic information from the parent. Variation and mutation are also included in the Mind Map. Go to EdrawMind to see more details on this template!
Edited at 2022-07-05 12:58:55
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Mendelian genetics - Heredity Part II
Introduction to heredity
gene
a section of dna at a specific location on the chromosome
contains information that determines a trait
mendelian trait
single trait determined by 1 gene
somatic cell
any cell in the body apart from gametes
Gamete
Sex cell
Hereditary traits and Genetics
hereditary trait
characteristic that can be passed on from one generation to another
examples:
wet or dry earwax
attached / detached earlobe
skin colour
hair colour
eye colour
blood type
face shape
chin shape
ability to roll tongue
Monohybrid Inheritance
inheritance of 1 characteristic with 2 contrasting forms controlled by a single gene
each gene is made up of a pair of alleles
alleles can be dominant or recessive
homologous chromosomes
exist in pairs where
one chromosome comes from the male parent
one chromosome comes from the female parent
both have the exact same gene loci
gene
unit of inheritance found on a particular locus of a chromosome
small portion of DNA in a chromosome that controls a particular characteristic or protein in an organism
alleles
alternative version of a gene that occupy the same locus on a pair of homologous chromosomes
can exist in 2 forms:
dominant
dominant allele will express itself in both homozygous dominant and heterozygous conditions
recessive
recessive allele will only express itself in a homozygous recessive genotype
Phenotype
traits of an organism that can be seen
influenced by genotype + environment
Genotype
genetic make-up of an organism that is inherited from its parents
Homozygous organism (for a certain trait)
happens if the 2 alleles controlling the trait are the same
possible combinations:
homozygous dominant (TT)
homozygous recessive (tt)
Heterozygous organism (for a certain trait)
happens if the 2 alleles controlling the trait are not the same
possible combination: Tt
Mendel's Monohybrid Experiment
Mendel cross-bred pure-bred Tall pea plants with pure-bred dwarf plants
F1 Generation hybrids all turned out to be tall plants
After the F1 offspring self - fertilized and produced seeds, F2 Generation plants came up
Ratio of tall plants to dwarf plants: 3 : 1(approx)
why?
genes are responsible for this
each charactersitic is controlled by a pair of factors in the cells
If the 2 factors are different, only the dominant factor will express itself
both the tall and short plants are pure bred
however, only the tall alleles were dominant and the short alleles were recessive
so when the 2 dominant tall gametes fused with the 2 recessive short gametes, the dominant alleles were expressed in heterozygous conditions while the recessive alleles were only expressed in homozygous conditions
this resulted in 1 dwarf and 3 tall hybrid plants
Genetic models
can be used to explain how alleles are passed on to offspring
predict the traits that will be displayed by the offspring
Sex Determination in humans
sex chromosomes
chromosomes that determine the sex of an organism
Autosomes
chromosomes in cells other than the sex chromosome
2 types of sex chromosomes:
X chromosome
Y chromosome
sex cells
cells that produce gametes by meiosis
somatic cells
other cells in the body
humans have:
22 pairs of autosomes
1 pair of sex chromosomes in each cells
XY - male
XX - female
male gametes
contain either the X or Y chromosome
Female gametes
contain only the X chromosome
how is the sex of the zygote determined?
if an X - carrying sperm fertilizes the ovum
the zygote will be female
if a Y - carrying sperm fertilizes the ovum
the zygote will be male
equal chance that the offspring could be male or female
Variation
differences in traits between individuals of the same species
traits of an individual are dependent on interactions between the genes and the environment
genetic variation
inheritable
variations due to environment
not inheritable
types of variations
continuous
deals with a range of phenotypes
controlled by many genes
occurs when 2 or more genes contribute to the final phenotype
genes show additive effect
alleles of a single gene combine and the combined affects show out as the phenotype
affected by environmental conditions
examples:
height
skin colour
caused by different levels of melanin in our skin
more alleles for melanin, darker skin (vice versa)
discontinuous
deals with a few clear-cut genotypes
genes do not show additive effect
not affected by environmental conditions
examples: eye colour, blood group
may arise due to:
crossing over and independent assortment of chromosomes and during meiosis
mutation in genetic material
provides new alleles to the gene pool for natural selection to act on
genetic variation is important to help organisms adapt and survive in changing environments
Mutations
change in structure of a gene (sickle - cell anemia) or in the chromosome number (Down's syndrome)
occurs as a result of error during the replication of the gene or chromosome
somatic mutations
occur in normal body cells
cannot be inherited
mutations can be inherited by the next generation if they occur in cells that give rise to gametes
dominant mutations
easily detected
recessive mutations
may not be detectable for generations
people will be carriers of it without anyone's knowledge
factors that increase the rate of mutations
radiation
chemicals
chromosome mutations
change in structure or number of chromosomes
example
Down's syndrome
aka Trisomy 21
people with this syndrome have an extra copy of chromosome 21
they have 47 chromosomes on total
normal humans have 46
how does this happen?
in rare cases when one of the eggs has 2 copies of chromosome 21
zygote formed has 3 copies of chromosome 21, so the child will have Down's syndrome
chromosome mutation in the gametes of a female parent can produce a child with Down's syndrome
gene mutations
change in the structure of DNA of a gene
produces variation between individuals as it results in new alleles of genes
examples
albinism
caused by a mutation in a recessive allele
absence of the pigment melanin results in reddish - white skin, white hair and pink eyes
albinos get sunburnt easily as they are very sensitive to sunlight
they can't look at the sun directly
sickle - cell anemia
caused by mutation in the gene controlling haemoglobin production
mutated gene is recessive, so it's only expressed in homozygous recessive conditions
how is the person affected?
sickle - shaped red blood cells have low oxygen carrying capacity and tend to clump together (and block blood flow)
fatal disease - sufferers usually die young
malaria caused by plasmodium
modifies red blood cells to obtain nutrients, escape destruction by splees
heterozygotes with both sickle - shaped and normal cells have an advantage
they are protected from malaria
they won't die due to lack of oxygen
such people are common in areas where malaria is prevelant like West Africa
Mutation and Selection
mutations can be:
harmful
individuals with harmful mutations will be eliminated
beneficial
individuals with beneficial mutation on the other hand may leave more offspring than normal individuals
nature "selects" organisms with more favourable characteristics to survive and reproduce
mutagens
can greatly increase the rate of mutations
rate of spontaneous mutatopn is extremely low in mutagens' absence
examples
radiation
UV light
X - ray
alpha and beta radiation
gamma rays
chemicals
mustard gas
formaldehyde
lysergic acid dielthylamide (LSD)