MYTUTOR SUBJECT ANSWERS

1284 views

What is an allele? What are dominant and recessive alleles?

The nucleus of a cell contains DNA molecules, which code for proteins. In humans, DNA is arranged into 46 linear, double-stranded molecules called chromosomes. Chromosomes of similar length are paired up – forming 23 pairs of chromosomes.

 

In a pair of chromosomes, each chromosome contains the same genes in (roughly) the same places. (A gene is a sequence of DNA that encodes for a protein, which controls a particular trait of a person.) For example, chromosomes A and B are together in a pair. The middle of chromosome A has genes for eye colour. The middle of chromosome B also has genes for eye colour.

 

However, genes can vary slightly. (eg. A gene can code for blue eye colour or brown eye colour.) A different version of the same gene is called an allele. In a pair of chromosomes, a person can either have two different alleles (heterozygous) or two of the same (homozygous).

 

Some alleles can be expressed if the person only has one copy of it. These are called ‘dominant’ alleles. For example, if a person has one allele for brown eyes and one allele for blue eyes, they will have brown eyes. (If they have two alleles for brown eyes, they will also have brown eyes.)

 

Some alleles can only be expressed if the person has two copies of it. These are called ‘recessive’ alleles. For example, if a person has two alleles for blue eyes, they will have blue eyes.

 

Basically:

 

Dominant allele + Dominant allele = Dominant trait (Homozygous dominant)

 

Dominant allele + Recessive allele = Dominant trait (Heterozygous dominant)

 

Recessive allele + Recessive allele = Recessive trait (Heterozygous recessive)

Christina T. Mentoring -Medical School Preparation- tutor, GCSE Biolo...

2 years ago

Answered by Christina, who has applied to tutor GCSE Biology with MyTutor


Still stuck? Get one-to-one help from a personally interviewed subject specialist

253 SUBJECT SPECIALISTS

£20 /hr

Teresa B.

Degree: Anatomy (Bachelors) - Glasgow University

Subjects offered:Biology, Spanish+ 3 more

Biology
Spanish
French
Chemistry
-Personal Statements-

“Since the dawn of time, I've been talking to people about things I love and enjoy. How cliché, I know. But don't roll your eyes at me yet. Hear me out: ...”

£30 /hr

Victoria S.

Degree: Physiology (Bachelors) - Liverpool University

Subjects offered:Biology, Maths

Biology
Maths

“Here to help with last minute revision prep! I'm Tory, in my final year studying Physiology at Uni of Liverpool and am a 5* rated tutor here to suit your needs.”

Sahil M. A Level Biology tutor, GCSE Biology tutor, A Level Chemistry...
£20 /hr

Sahil M.

Degree: Medicine (Bachelors) - Manchester University

Subjects offered:Biology, Spanish+ 3 more

Biology
Spanish
Maths
Chemistry
-Medical School Preparation-

“Hello! My name is Sahil and I am currently a medical student at the University of Manchester. I am really looking forward to tutoring you in Spanish, Chemistry, Biology or Maths as well as trying to help you during the difficult proce...”

About the author

Christina T.

Currently unavailable: for new students

Degree: Dentistry (Bachelors) - Bristol University

Subjects offered:Biology, Human Biology+ 1 more

Biology
Human Biology
-Medical School Preparation-

“Top tutor from the renowned Russell university group, ready to help you improve your grades.”

MyTutor guarantee

You may also like...

Other GCSE Biology questions

1 a) What is a pathogen? 1 b) How do white blood cells help to defend the body against pathogens?

What are the different ways in which substances can move across cell membranes?

How does the structure of the red blood cell allow it to carry out its functions?

What is a proposed model for enzyme activity?

View GCSE Biology tutors

We use cookies to improve your site experience. By continuing to use this website, we'll assume that you're OK with this. Dismiss

mtw:mercury1:status:ok