7A Genes and Chromosomes Flashcards
Explain what DNA is
DNA = a double-stranded nucleic acid chain made up of nucleotides. DNA carries the instructions for proteins which are required for cell and organism survival. DNA is genetic information (genome) and packaged into chromosomes
Explain what a gene is?
Gene = a section of DNA that carries a code to make a protein, they are the basic biological unit made up of specific sequence of deoxyribonucleic acids, they carry all of the genetic instructions .
Explain what an allele is?
Allele = alternate form of a gene
If all alleles are the same what are they called?
Homozygous – identical alleles
If the alleles are different, what are they called?
Heterozygous – different alleles
Explain what a genome is?
Genome = the entire set of genetic instructions of an organism.
Explain what a chromosome is? What are they made up of?
Chromosome = the structure made of protein and nucleic acids that carries genetic information, coiled and packaged DNA strands for cell division; each individual gene has its own gene locus on the chromosome. Made up of genes which are made up to DNA, which are made up of nucleotides
What is in a diploid cell? What is an example of a diploid cell?
Diploid = 2 sets of chromosomes,
A cell possessing two copies of each chromosome (human body cells).
What is a haploid cell? What is an example of a haploid cell?
Haploid = one set of chromosomes,
A cell possessing a single copy of each chromosome (human sex cells).
How many matching pairs of chromosomes are there in humans?
22 matching pairs
What are the 22 matching pairs of chromosomes called?
22 matched pairs of chromosomes – autosomes
What are the last pair, 23rd pair of chromosomes called
23rd pair – sex chromosomes
For the DNA structure, what is DNA made up of? What do these consist of? Which is the head and which is the tail?
Made of nucleotides, Nucleotide are made up of Sugar (tail), Phosphate (head) group and Nitrogenous base
Is the sugar and phosphate the same in all nucleotides?
Yes
What are the matching bases in DNA
Adenine matches with Thymine, and Cytosine matches with Guanine
What is nucleic acid?
Nucleic acid: compound, such as DNA or RNA, built from nucleotide sub-units
Explain the double helix structure of DNA?
2 anti parallel nucleotide chains where the nucleotides facing inward and sugar phosphate backbones facing outside,
What bonds are formed in the double helix?
Weak hydrogen bonds between the base pairs. Double bond between adenine and thymine, triple bond between cytosine and guanine.
What is the length of DNA expressed by?
Length of DNA is expressed by number of base pairs (bp)
How many base pairs does a human cell chromosome on average?
120 million bp
How many base pairs are in the average gene length?
3000 bp
How many genes make up a human genome?
20000 - 25000
What are gene loci?
The position occupied by a gene is its locus (plural: loci)
What has more DNA, eukaryotic cell or prokaryotic cell? By how much?
Eukaryotic, by about 1000 times more
How is the DNA organised in an eukaryotic cell and in a prokaryotic cell?
The DNA in a eukaryotic cell is organized into several linear chromosomes, it’s organization is much more complex than the single, circular DNA molecule in a prokaryotic cell
How do chromosomes in eukaryotic cell or prokaryotic cell differ?
Eukaryotic
* many chromosomes
* linear chromosomes
* made of chromatin, a nucleoprotein (DNA coiled around histone proteins)
* found in a nucleus
* copies chromosomes, then the cell grows, then goes through mitosis to organise chromosomes in two equal groups
Prokaryotic
* single chromosome plus plasmids
* circular chromosome
* made only of DNA
* found in cytoplasm
* copies its chromosome and divides immediately afterwards
How many chromosomes does a human have? How many chromosomes does a dog have? How many does earth worm, and a horse round worm have?
Humans 46 (2n = 26), Dogs 78 (2n = 78), Earth worm 36 (2n = 36).
Horse worm 4
To determine the sex of a human, what order of chromosomes are for female and for male?
Female XX
Male XY
Are the chromosomes all the same size?
No, our genetic information is stored in 23 pairs of chromosomes that vary widely in size and shape. Chromosome 1 is the largest and is over times bigger than chromosome 2.
Are organisms with a larger number of chromosomes more complex?
No, the number of chromosomes in an organism is not related to how complex it is.
Is the human X chromosome that same size as the human Y chromosome?
No, the human X chromosome is three times larger than the human Y chromosome
What are chromosomes composed of?
Chromosomes are composed of a complex of DNA and protein called chromatin that condenses during cell division
How many DNA does an unduplicated chromosome contain?
Each unduplicated chromosome contains one DNA molecule, which may be several inches long
How is a nucleosome formed?
Every 200 nucleotide pairs, the DNA wraps twice around a group of 8 histone proteins to form a nucleosome.
How are the sex chromosome represented?
Are represented as X and Y
What is for a female and for a male?
Females have two large X chromosomes and Males have a large X and a small Y chromosome
Explain the features of a chromosome- telomeres
Telomeres - a region of repetitive base sequences that is found at the end of every chromosome. used to protect the ends of chromosomes from fusing with other nearby chromosomes in the nucleus
Explain the features of a chromosome- DNA Molecule
DNA molecule - each chromosome is composed of a long DNA molecule that has been coiled tightly around histone proteins
Explain the features of a chromosome- centromere
Centromere - a specialised sequence of DNA that holds together the two chromatids, The centromere is a constricted region of the chromosome containing a specific DNA sequence, to which is bound 2 discs of protein called kinetochores.
Explain the features of a chromosome- sister chromatids
Sister chromatids the identical daughter strands of a replicated chromosome
Explain the features of a chromosome- short arm and long arm?
Short arm - aka ‘p arm’ – this is the section of the chromosome that is shorter in length
Long arm - aka ‘q arm’ – this is the section of the chromosome that is longer in length homologous chromosomes
What are homologous chromosomes?
Chromosomes with the same length, gene loci, and centromere position.
What happens during chromosome duplication?
- In preparation for cell division, DNA is replicated and the chromosomes condense
- Each duplicated chromosome has two sister chromatids, which separate during cell division
What is a karyotype?
A karyotype is a photograph of a person’s chromosomes lined up in order of size from largest to smallest.
What can karyotypes be used to determine?
A karyotype can be used to determine species, sex, and some genetic abnormalities
How are pairs of chromosomes ordered in a karyotype?
Pairs of chromosomes in a karyotype are arranged from largest to smallest.
How can a karyotype be used as a visual representation to identify chromosome abnormalities?
A karyotype is helpful in determining whether an individual has a chromosome abnormality since it is a visual representation of all of the chromosomes that the organism has. Once homologous chromosomes are paired up, it is easy to see if one is missing or if there is an extra chromosome present.
What are three things a karyotype can tell you?
A chromosomal karyotype is used to detect chromosome abnormalities and thus used to diagnose genetic diseases, some birth defects, and certain disorders of the blood or lymphatic system.
What disorders or abnormalities can a karyotype tell you?
Some disorders or abnormalities can a karyotype tell you include
* Down syndrome (trisomy 21). A baby has an extra, or third, chromosome 21. This affects how the baby looks and learns.
* Edwards syndrome (trisomy 18). A baby has an extra 18th chromosome. These babies usually have many problems, and most don’t live longer than a year.
* Patau syndrome (trisomy 13). A baby has an extra 13th chromosome. These babies usually have heart problems and severe mental impairment. Most won’t live more than a year.
* Klinefelter syndrome. A boy baby has an extra X chromosome (XXY). They may go through puberty at a slower pace, and may not be able to have children.
* Turner syndrome (monosomy). A girl baby has a missing or damaged X chromosome. It causes heart problems, neck problems, and short height.
What is Aneuploidy?
Aneulploidy is when a cell or organism varies in the usual number of chromosomes in its genome by the addition or loss of a chromosome
It is caused by non-disjunction: the failure of homologous chromosomes or sister chromatids to separate properly during cell division (meiosis - anaphase 1)
Explain the difference in and give an example for: monosomy aneuploidy
Monosomy one missing chromosome (2n-1) e.g. turner syndrome - single chromosome X, fused neck
Explain the difference in and give an example for: trisomy aneuploidy
Trisomy one extra chromosome (2n+1) e.g. down syndrome - extra copy of chromosome 21, delayed physical growth e.g. Klinefelter syndrome - extra X chromosome in males (XXY), small testes
Explain the difference in and give an example for: tetrasomy aneuploidy
Tetrasomy two extra chromosomes (2n+2) e.g. Tetrasomy X - two extra copies of the X chromosome, mild delay in physical development
Explain the difference in and give an example for: polyploidy aneuploidy
Polyploidy when an organism contains additional sets of chromosomes in its genome more common in plants - one advantage of polyploidy includes increased size and hardness in certain types of fruit
How is the inheritance of gender determined?
Of the XX female and XY male, there is 50/50 chance of either sex
LOOK AT THE QUESTIONS ON THE DNA REVISION WORKSHEET
LOOK AT THE QUESTIONS ON THE DNA REVISION WORKSHEET
