biology exam revision Flashcards
what is inheritance?
the study of how genes are passed from parents to offspring
who discovered inheritance?
Gregor Mendel
what is a dominant allele
an allele that masks/hides recessive alleles
what is a recessive allele
A allele that is only seen in the absence of a dominant allele
what is an allele
a variation of a gene
what is a gene?
A small segment of DNA that controls what characteristics an organism has.
what does DNA stand for?
Deoxyribo nucleic acid.
what makes up a nucleotide?
one phosphate, one deoxyribose sugar and one nitrogenous base.
In diagrams on a nucleotide, what shape normally represents the phosphate?
the circle
In diagrams on a nucleotide, what shape normally represents the deoxyribose sugar?
A pentagon
In a DNA ladder… what makes up the steps?
nitrogenous bases
Where is DNA located in a cell?
the nucleus
When DNA is loosely condensed and wrapped into a wool like structure what is it called?
chromatin
When DNA is tightly condensed and packaged. What is it called?
chromosome
How many chromosomes are in a normal human cell?
46 chromosomes
How do nitrogenous bases bond together?
via hydrogen bonding
how many nitrogenous based are there?
4
What are the four letter that represent nitrogenous bases?
A, T, C, G
What is the name of the nitrogenous base A?
Adenine
What is the name of the nitrogenous base T?
Thymine
What is the name of the nitrogenous base C?
Cytosine
What is the name of the nitrogenous base G?
Guanine
Which bases pair together?
A and T
C and G
What makes up the backbone of DNA?
Phosphates and deoxyribose sugars
what is the purpose of DNA replication?
To create multiple copies of identical DNA
What are the 3 stages of DNA replication
- straightening and separating of DNA (denaturation)
- cloning (DNA synthesis)
- Checking for errors
What occurs in the first stage of DNA replication?
-An enzyme breaks apart the hydrogen bonds between the nitrogenous base pairs.
-The two DNA strands separate and unwind
-This exposes the nitrogenous bases
hat occurs in the second stage of DNA replication?
-In the nucleus there is free floating nucleotides
-The free floating nucleotides bond to the exposed nitrogenous bases (hydrogen bonding)
-An enzyme binds the DNA backbone backbone in the new DNA strand
-This creates 2 new DNA strands that are identical. (They both have 1 of the original strand and 1 of the newly made strand)
What occurs in the third stage of DNA replication?
An enzyme proof-reads that DNA strand and checks for any errors.
Any errors are fixed.
What is the centre part of a chromosome called?
A centromere
How do you count chromosomes?
by the number of centromere
What is half a chromosome called?
a chromatid
Two chromatids that join in the middle can be called what?
sister chromatids
Chromosomes can be single stranded or double stranded.. how many copies of DNA are in each type?
ingle- 1 copy
double- 2 copies
What is a karyotype?
A picture of all the chromosomes in an organism’s genome
In a human karyotype, the first 22 chromosome pairs are…?
autosomal
-determine general traits
In a human karyotype, the 23rd/last chromosome are…?
sex chromosomes
What are male sex chromosomes?
XY
What are female sex chromosomes?
XX
What occurs is pre- mitosis?
interphase
What occurs in interphase in mitosis and meiosis one ?
-DNA replicates
-single stranded chromosomes become double.
-Chromatin become visible.
What occurs in prophase of mitosis and meiosis?
The nuclear membrane breaks down
-spindle fibres appear
-Chromatin condense into chromosomes
What occurs in metaphase of mitosis?
-chromosomes line up in the equator of the cell
-Spindle fibres attach to the centromere of chromosomes
What occurs in metaphase of meiosis 1?
-Homologous chromosome pairs line up in two lines along the equator of the cell
-Spindle fibres attached to chromosomes.
What is the difference between metaphase 1 and metaphase 2 of meiosis?
In metaphase 1, Homologous chromosomes line up in pairs along the equator.
whereas,
In metaphase 2, a single line of doubles stranded chromosomes lines up along the equator.
What occurs in anaphase of mitosis?
-The spindle fibres contract/shorten
-The double stranded chromosomes are ripped apart into single stranded chromosomes (chromatid).
- The chromatid move to opposite poles of the cell
What is the difference between anaphase 1 and 2 in meiosis?
In Anaphase 1, spindle fibres separate a homologous chromosome pair. One double stranded chromosome moves to each pole of the cell.
whereas,
-In Anaphase 2, spindle fibres rip apart a double stranded chromosome into single stranded chromosomes (chromatid). one chromatid moves to opposite poles of the cell.
what occurs in telophase during mitosis and meiosis?
Two new nuclear membranes are formed
-Spindle fibres disappear
- chromosomes unwind into chromatin
What occurs during cytokenesis?
The cytoplasm pinches in half and becomes 2 separate cells.
What phase occurs in meiosis 1 and not meiosis 2?
interphase
Why are gametes haploid?
so that when they fuse during fertilisation, they become diploid.
What does haploid mean?
A cell with 1 copy of DNA
What does diploid mean?
A cell with 2 copies of DNA
What types of cell does mitosis produce?
diploid
What types of cell does meiosis produce?
haploid
Are cell produced from mitosis identical or genetically different?
identical
Are cell produced from meiosis identical or genetically different?
genetically different
What is the purpose of meiosis?
Sexual reproduction
-producing gametes
What is the purpose of mitosis?
What is the purpose of mitosis?
How many cells are created from mitosis?
2
How many cells are created from meiosis?
4
what times do cell spend the most time in?
interphase
What is the difference between mitosis and cytokenesis?
-mitosis is the separation of the nucleus
whereas,
-cytokinesis is the separation of the cytoplasm/cell
