Unit 5: Heredity

What does it mean by replicated DNA is ‘semi-conservative’

One strand is from the original, the other is newly made

What does helicase do?

unwinds and separates DNA strand by breaking hydrogen bonds

What does DNA polymerase do?

covalently joins free nucleotides together

because DNA strands can be very long, DNA replication ____

occurs at multiple places simultaneously

polymerase chain reaction is a:

technique to amplify fragments of DNA

outline steps of PCR

1. denaturation: DNA is heated to break h-bonds of double strands

2. annealing: sample is cooled down and short primers bond to complementary sequences in DNA sample

3. extension phase: sample is heated up; bonding of primers allows Taq polymerase to replicate DNA using primers as starting point

what is gel electrophoresis?

a method to separate DNA fragments by size to identify key features

outline how gel electrophoresis works

1. samples of DNA fragments are loaded into depressions on one end of the gel

2. gel is submerged in buffer solution

3. electric current runs through gel

4. dna will start at negative pole and move to positive pole

   1. smaller strands move faster so it separates

what is DNA profiling?

individuals can be identified by their DNA profiles

what is short tandem repeats?

different people have different repeats of STR, so it makes unique DNA profiles

how is dna profiled?

• dna sample collected

• amplified using pcr

• STR loci is cut out (fragments)

  • fragments separated by gel electrophoresis and then compared

What happens in ‘interphase’ of the cell cycle (how does cell prepare for division)

1. grow

2. DNA replication

3. preparation

what are sister chromatids?

(during DNA replication) chromosomes temporarily consist of 2 DNA molecules

sister chromatids are joined by …

centromere

mitosis is…

nuclear division

outline interphase of mitosis:

DNA is replicated to form two identical chromatids (uncondensed)

outline prophase (mitosis)

DNA supercoils and condenses
Nuclear membrane dissolves
Centrosomes move to poles and produce spindle fibers

Outline metaphase (mitosis)

Spindle fibers connect to centromere (Center of sister chromatids)

Chromosomes move to form a line in the middle of cell

Spindle fibers begin to shorten

Outline anaphase (mitosis)

Sister chromatids separate as they’re dragged to poles by spindle fibers

Sister chromatids now separate identical chromosomes

Outline telophase (mitosis)

Chromosomes decondense becoming chromatid again

Nuclear membrane forms around two chromosome sets

Outline cytokinesis

animals: microtubule fibers form cleavage furrow and splits the middle

plants: vesicles form and fuse to form an end plate

meiosis is…

how haploid sex cells are produced in reproductive organs

haploid cell is…

sperm and egg. containing only one chromosome

meiosis creates:

4 distinct haploid cells (genetic variation)

mitosis creates:

two identical diploid cells (cloning)

in prophase 1 (meiosis) ,

4 homologous chromosomes (2 pairs from mum and dad) connect and become 2 bivalent

in metaphase 1 (meiosis),

nucleus breaks down, the two bivalents then line up at equator

in anaphase 1 (meiosis),

spindle fibers separate bivalents and pull sister chromatids to poles (2 pairs at each pole)

telophase 1 and cytokinesis 1 (meiosis) is..

the same as mitosis

metaphase 2 is…

the same as mitosis and forms 4 haploid cells

genetic variation occurs in meiosis through:

1. crossing over

   1. individual assortment

describe crossing over

1. in prophase 1

2. exchange of DNA segments between homologous pairs

3. all four chromatids of the homologous pairs become genetically distinct, leading to new phenotypic variants

describe random assortment

1. in metaphase 1

2. homologous chromosomes line up at equator at random orientation

3. different combinations form as a result (within the gametes produced)

non-disjunction is…

when a homologous pair fails to separate (in anaphase 1 or 2)

non disjunction leads to:

• less or more chromosome

  • Down syndrome: one extra chromosome 21

an autosome is..

chromosome that always appears in a pair (not sex chromosome)

homologous pairs are virtually identical, except:

at each gene locus their alleles may be different

sex chromosomes are called…

heterosomes

allels are:

alternative forms of genes

genotype is…

The complete set of alleles that a given organism has

homozygous genotype is when:

homologous pair has same alleles

heterozygous genotype is when..

homologous pair has different alleles

hemizygous is:

for men who only have one copy of sex allele

phenotype is:

observable characteristics of an individual , influenced by genotype and environment

epigenetics is…

differences to phenotype caused by changes in gene expression

phenotypic plasticity is:

ability for phenotype to shape based on environment

give an example of phenotypic plasticity

seasonal polyphenism in some buterflies; changes in wing pattern in different seasons

codominance is..

both alleles are equally dominant, so both are expressed

incomplete dominance is..

when neither are strong so it results in a blended phenotype

Recessive alleles need ___ to show up

to be homozygous for it

X linked dominant is more common in

women (because they get x chromosome from dad)

X linked recessive is more common in

men because they only have one copy (cannot be carriers)

An example of x linked recessive disorder is

haemophillia (cant clot blood) and color blindness

if both parents are affected but one kid is not,

the disease is autosomal dominant, and the parents are both heterozygous. the child is homozygous recessive.

if both parents are unaffected and one kid is affected,

the disease is autosomal recessive. parents are heterozygous and child is homozygous recessive.

polygenic traits…

have continuous variation (because affected by multiple genes)