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Biology > Inheritance > Flashcards

Inheritance Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What are homologous chromosomes?

A
  • two chromosomes that carry the same GENE in the same positions
  • same shape
  • (same gene, not necessarily allele)
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2
Q

What is meiosis?

A
  • nuclear division
  • results in the production of four daughter cells with HALF the chromosome number of the parent cell
  • and reshuffled alleles
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3
Q

Describe Prophase 1

A
  • chromosomes condense, become visible
  • nuclear envelope disappears
  • nucleolus disappears
  • centrioles migrate to poles
  • microtubules assemble
  • homologous chromosomes pair up forming a bivalent
  • crossing over occurs at chiasmata
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4
Q

How does crossing over lead to genetic variation?

A
  • occurs in prophase 1
  • homologous chromosomes pair up forming a bivalent
  • crossing over: exchange of alleles between non-sister chromatids of homologous chromosomes
  • this occurs at the CHIASMA (position)
  • linkage groups broken
  • results in new combinations of alleles
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5
Q

Describe metaphase 1

A
  • bivalents line up along equator of spindle, attached by centromeres
  • random alignment
  • each pair lines up independently of each other
  • 2^n combinations
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6
Q

How does independent assortment lead to genetic variation? (meiosis 1)

A
  • homologous chromosomes line up randomly on equator
  • this produces many chromosome combinations
  • 2^n combinations
  • new combinations of maternal and paternal alleles
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7
Q

What is reduction division?

A
  • only meiosis 1 is a reduction division
  • since there was a reduction in chromosome number
  • original cell was diploid, but after meiosis 1, 2 cells formed are haploid
  • after meiosis 2, 4 haploid cells are produced
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8
Q

What is the gene locus?

A
  • the position of a gene on a chromosome
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9
Q

What is an allele? (3 marks)

A
  • a variety/alternative form of a gene
  • determines one form of a characteristic
  • occupies same gene locus
  • sequence of bases
  • can be dominant or recessive
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10
Q

What is a gene?

A
  • a small length of DNA on a chromosome
  • which codes for a particular polypeptide
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11
Q

What are the genotypes and phenotypes of an organism?

A

Genotype: the alleles possessed by an organism (e.g BB)
Phenotype: the observable features of an organism, affected by genes AND environment (e.g Brown coat)

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12
Q

What is a dominant allele?

A
  • An allele that has always has an effect on phenotype if present
  • expressed in BOTH homozygous and heterozygous individuals
  • e.g BB and Bb both brown coat
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13
Q

What is a recessive allele?

A
  • An allele that only affects phenotype if NO dominant allele is present
  • only expressed in homozygote
  • e.g bb is white coat
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14
Q

What is codominance?

A
  • codominant alleles both affect the phenotype when both alleles are present
  • e.g blood group
  • allele A and B = dominant
  • allele O = recessive
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15
Q

What is monohybrid inheritance?

A
  • inheritance of one gene
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16
Q

What are F1 and F2 crosses?

A

F1 cross: offspring resulting from the cross between individuals with homozygous recessive and homozygous dominant genotype
- homozygous recessive x homozygous dominant = heterozygous offspring

F2 cross: offspring resulting from a cross between F1 offspring
- heterozygous offspring x heterozygous offspring

17
Q

How is a test cross carried out?

A
  • organism showing dominant characteristic
  • is crossed with a homozygous recessive organism
  • the phenotypes of the offspring can indicate whether the original organism is homozygous or heterozygous
18
Q

What is a sex-linked gene?

A
  • a gene found on a region of a sex chromosome that is not present on other sex chromosomes
  • in humans, most sex-linked genes are found on X chromosome
  • sex chromosome: X and Y
19
Q

What is a carrier?

A
  • an individual who possesses a particular allele as a single copy
  • the effect of this allele is masked by the dominant allele
  • so the organism will not display the characteristic in its phenotype
  • however can be passed to offspring, who can display the characteristic
  • females can be carriers, whereas males cannot
20
Q

What is dihybrid inheritance?

A
  • inheritance of two genes
21
Q

What is epistasis?

A
  • the interaction of two genes at different loci; one gene may affect the expression of the other
22
Q

What is autosomal linkage?

A
  • the presence of two genes on the same autosome (any chromosome other than sex chromosome)
  • so they tend to be inherited together and do not assort independently
23
Q

What is parental type and recombinant genotype?

A
  • parental type: offsprings that show the same combinations of characteristics as parents
  • recombinant: offspring that show different combinations of characteristics from their parents (due to crossing over in prophase 1)
24
Q

What is the chi-squared test used for?

A
  • a statistical test that is used to determine whether differences between observed and expected results are a significant
25
Q

What are the causes of albinism?

A
  • gene: TYR
  • albinism is a lack of melanin in skin, eyes and hair

normal process:
- normal gene codes for enzyme called tyrosinase
- tyrosine is converted to DOPA/dopaquinone (by tyrosinase)
- which results in formation of melanin
- in melanocytes

mutant allele:
- mutant allele is recessive
- tyrosinase is not produced/inactive
- affects skin/hair
- only in homozygous recessive people

26
Q

What are the causes for sickle cell anemia?

A
  • gene: HBB
  • HBB codes for amino acid sequence in B-globin polypeptide

mutant allele:
- recessive
- homozygous for mutant allele (HbS)
- CTT replaced with CAT
- glutamic acid to valine
- results in an altered B-polypeptide in haemoglobin
- haemoglobin is less soluble in lower oxygen concentrations
- red blood cells sickle
- so RBC carry less oxygen
- get stuck in capillaries
- clump together and block blood flow

pros:
- protection against malaria

27
Q

What are the causes of haemophilia?

A
  • gene: F8
  • Factor 8 protein plays a role in blood clotting
  • synthesized in liver cells

Mutant F8 allele:
- sex-linked gene
- homozygous recessive
- abnormal F8 alleles result in:
- production of abnormal factor 8 protein
- less production of normal factor 8 protein
- no production at all

28
Q

What causes Huntington’s disease?

A

Huntington’s is a neurological condition
- brain neuron degeneration
- involuntary movements, uninhibited motor control

Mutant allele: HTT
- DOMINANT
- mutation on chromosome 4
- normal allele has 10-35 repeating CAG units
- dominant allele has extra CAG repeats
- usual onset is middle age

29
Q

What is a structural gene?

A
  • gene that codes for a protein with a specific function within a cell
30
Q

What is a regulatory gene?

A
  • codes for a protein that helps control expression of other genes
  • e.g repressor protein in prokaryotes, transcription factors in eukaryotes
31
Q

What genes are present in the lac operon?

A

regulatory gene
- lac I: codes for repressor protein

structural genes
- lac Z: codes for B-galactosidase (lactase)
- lac Y: codes for permease (allows lactose to enter cell)
- lac A: codes for acetyl transferase

32
Q

How is gene expression controlled in prokaryotes?

A

Lactose absent:
- repressor protein binds to operator
- so RNA polymerase unable to bind to promoter
- transcription of structural genes cannot occur
- enzymes and proteins cannot be synthesized

Lactose present:
- lactose binds to repressor protein
- distorting its shape
- so it can no longer bind to operator
- RNA polymerase able to bind to promoter
- transcription occurs

33
Q

What is a transcription factor?

A
  • a molecule that affects whether a gene is expressed or not
34
Q

What is an inducible enzyme?

A
  • an enzyme that is synthesized only when a substrate is present
  • can be switched on/off
  • causes gene expression

e.g B-galactosidase enzyme synthesized when lactose is present

35
Q

What is a repressible enzyme?

A
  • an enzyme that is normally produced, and whose synthesis is prevented in the presence of an effector
  • effector binds to/ activates repressor protein and allows repressor to bind to operator
  • end-product inhibition
36
Q

How is gene expression controlled in eukaryotes?

A
  • Control of seed germination, done by plant hormone called Gibberellin
  • influences transcription of amylase enzyme

Gibberellin absent:
- Repressor protein DELLA bound to PIF
- PIF can NOT bind to promoter
- no transcription occurs

Gibberellin present:
- Gibberellin binds to receptor of an enzyme
- this causes the DELLA repressor protein to break down
- PIF CAN bind to promoter
- transcription can occur
- amylase produced, seed germinates

37
Q

What is the genome?

A
  • ALL the genetic material/DNA present in an organism
  • combined nuclear and mitochondrial DNA

Biology (9 decks)

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